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COPYRIGHT DEPOSm 



TUNNELING: 



A PRACTICAL TREATISE 



BY 

CHARLES PRELINI, C. E. 

AUTHOR OF "earth AND ROCK EXCAVATION," "DREDGES AND DREDGING, 

"earth slopes, retaining walls and dams," etc. professor 

OF civil engineering in MANHATTAN COLLEGE, 
NEW YORK 



167 ILLUSTRATIONS 



SIXTH EDITION, REVISED AND ENLARGED 




NEW YORK 

D. VAN NOSTRAND COMPANY 

Twenty-five Park Place 
1912 



H 






Copyright, 1912, 

BY 

D. VAN NOSTRAND COMPANY 

NEW YORK 




y 





Stanbope iptess 

F. H. GILSON COMPANY 
BOSTON. U.S.A. 



^ i*'^ 



^ PREFACE TO THE SIXTH EDITION 



During the few years that have elapsed since the pubhca- 
tion of the first edition of this work, the art of tunnehng 
through different soils and especially under large bodies of 
water, has made considerable progress. During the last 
ten years, no less than eight subaqueous tunnels involving 
the construction of sixteen tubes have been constructed for 
the service of the city of New York alone. The reader will, 
no doubt, also recall the tunnels under the Boston Harbor, 
the St. Clair, the Charles and Detroit Rivers in our own 
country as well as the tunnels under the Thames and the 
Seine in Europe. Engineers, contractors and workmen have 
acquired such experience in these difficult underground and 
under-river construction that the work is now undertaken 
without any of the fear and hesitation that were associated 
with the earlier enterprises. 

As entirely new methods have been introduced by pro- 
fessional men, it was found necessary to arrange the pres- 
entation of the subject in this sixth edition so as to give 
due prominence to these recent methods. 

Besides this, other changes have been made in order to 
give greater attention to American method of excavating 
tunnels through rock and loose soil. This will explain the 
treatment of the crown-bar and also the extensive illustra- 
tion of the heading and bench method as well as the drift 
method of driving tunnels which is followed in the United 
States. 

Space has also been given to important tunnels recently 
built mainly for the purpose of illustrating the various 

iii 



IV PREFACE 

methods discussed in the text and also to bring out more 
clearly the characteristics of the different methods of tunnel 
excavation. 

The author hopes that these added features will meet the 
present requirements of engineers and students. 

Charles Prelini. 

Manhattan College, 

New York City. 



CONTENTS 



PAGE 

INTRODUCTORY — The Historical Development op Tunnel 

Building xiii 

CHAPTER 

I. Preliminary Considerations; Choice between a Tunnel 

and an Open Cut; Geological Surveys 1 

II. Methods of Determining the Center Line and Forms and 

Dimensions op Cross-Section 9 

III. Excavating Machines and Rock Drills; Explosives and 

Blasting 22 

IV. General Methods op Excavation; Shapts; Classipication 

OP Tunnels 36 

V. Methods op Timbering or Strutting Tunnels .... 47 

VI. Methods of Hauling in Tunnels 59 

VII. Types of Centers and Molds Employed in Constructing 

Tunnel Linings of Masonry 66 

yill. Methods op Lining Tunnels 72 

IX. Tunnels through Hard Rock; General Discussion; 
Representative Mechanical Installations for Tun- 
nel Work 84 

X. Tunnels through Hard Rock {continued) ; Excavation by 

Drifts; The Simplon and Murray Hill Tunnels . . 102 
XI. Tunnels through Hard Rock {continued) ; Excavation by 

Headings 130 

XII. Excavating Tunnels through Soft Ground; General 

Discussion; The Belgian Method 143 

XIII. The German Method — Excavating Tunnels through 

Soft Ground {continued) ; Baltimore Belt Line Tunnel 155 

XIV. The Full Section Method of Tunneling; English 

Method; American Method; Austrian Method . . . 166 
XV. Special Treacherous Ground Method; Italian Method; 

Quicksand Tunneling; Pilot Method 182 

V 



VI 



CONTENTS 



CHAPTER 

XVI. 



XVII. 

XVIII. 



XIX. 
XX. 



XXI. 



XXII. 

XXIII. 
XXIV. 

XXV. 



Open-Cut Tunneling Methods; Tunnels under City 
Streets; Boston Subway and New York Rapid Tran- 
sit 195 

Submarine Tunneling; General Discussion; The Severn 
Tunnel 218 

Submarine Tunneling {continued)', The Compressed Air 
Method; The Milwaukee Water-Works Tunnel . . 225 

Submarine Tunneling {continued)] The Shield System . 238 

Submarine Tunneling {continued)] The Shield and Com- 
pressed Air Method; The Hudson River Tunnel of 
THE Pennsylvania Railroad 263 

Submarine Tunneling {continued) ; Tunnels at very Shal- 
low Depth; The Cofferdam Method; The Pneumatic 
Caisson Method; The Joining Together Sections of 
Tunnels Built on Land 281 

Accidents and Repairs in Tunnels during and after Con- 
struction 301 

Relining Timber-Lined Tunnels with Masonry .... 315 

The Ventilation and Lighting of Tunnels during Con- 
struction 325 

The Cost of Tunnel Excavation and the Time Required 
FOR Work 336 



LIST OF ILLUSTRATIONS 



TIGURE PAGE 

1. Diagram Showing Manner of Lining in Rectilinear Tunnels 10 

2. B. R. Value's Device for Locating the Center Line Inside of a 

Tunnel 11 

3. Triangulation System for Establishing the Center Line of the St. 

Gothard Tunnel , 12 

4. Method of Transferring the Center Line down Center Shafts 13 

5. Method of Transferring the Center Line down the Side Shafts ... 14 

6. Method of Laying out the Center Line of Curvihnear Tunnels ... 15 

7. Diagram of Polycentric Sectional Profile 19 

8. 9 and 10. Typical Sectional Profiles for Tunnel 20 

11. Soft Ground Bucket Excavating Machine; Central London Under- 

ground Railway 22 

12. Column Mounting for Percussion Drill; IngersoU Sargent Drill Co. 26 

13. Sketch of Diamond Drill Bit 27 

14. Diagram Showing Sequence of Excavation for St. Gothard Tunnel . 36 

15. Diagram Showing Manner of Determining Correspondence of Exca- 

vation to Sectional Profile 38 

16. Polar Protractor for Determining Profile of Excavated Cross- 

Section 39 

17. Joining Tunnel Struts by Halving 48 

18. Round Timber Post and Cap Bearing 48 

19. Ceiling Strutting for Tunnel Roofs 49 

20. Ceiling Strutting with Side Post Supports 49 

21. Sill, Side Post and Cap Cross Frame Strutting 49 

22. Reinforced Cross Frame Strutting for Treacherous Materials 49 

23. Longitudinal Poling-Board System of Roof Strutting 50 

24. Transverse Poling-Board System of Roof Strutting 50 

25. Shaft with Single Transverse Strutting 52 

26. Rectangular Frame Strutting for Shafts 53 

27. Reinforced Rectangular Frame Strutting for Shafts in Treacherous 

Materials 53 

vii 



Vlll LIST OF ILLUSTRATIONS 

FIGtTRB PAGE 

28. Strutting of Timber Posts and Railway Rl"' Caps 56 

29. Strutting Made Entirely of Railway Rails 56 

30. Rziha's Combined Strutting and Centering of Cast Iron 57 

31. Cast-iron Segment of Rziha's Strutting and Centering 57 

32. Cast-Iron Segmental Strutting for Shafts 58 

33. Platform Car for Tunnel Work 59 

34. Iron Dump-Car for Tunnel Work 60 

35. Wooden Dump-Car for Tunnel Work 60 

36. Box-Car for Tunnel Work 61 

37. Elevator Car for Tunnel Shafts 65 

38. Ground Mold for Constructing Tunnel Invert Masonry 67 

39. Combined Ground Mold and Leading Frame for Invert and Side 

Wall Masonry 67 

40. Leading Frame for Constructing Side Wall Masonry 68 

41. Plank Center for Constructing the Roof Arch 69 

42. Trussed Center for Constructing the Roof Arch 70 

43 and 44. A Tjrpical Form of Timber Lining for Tunnels 73 

45. Diagram Showing Forms adopted for Side- Wall Foundations 76 

46 and 47. Transverse Sections of Tunnels Showing Methods for In- 
creasing the Thickness of the Lining at Different Points 79 

48. Refuge Niche in St. Gothard Tunnel 81 

49. East Portal of Hoosac Tunnel 82 

50. 51 and 52. Arrangement of Drill Holes in the Heading of Turchino 

Tunnel 91 

53 and 54. Arrangement of Drill Holes in the Heading of the Fort 

George Tunnel 91 

55. Diagram Showing Sequence of Excavations in Drift Method of 

Tunneling Rock 102 

56. Sketches Showing Sequence of Work in Excavating and Lining the 

Simplon Tunnel Ill 

57. General Details of the Brandt Rotary Drills Employed at the 

Simplon Tunnel 112 

58. Sequence of Excavation in the Murray Hill Tunnel 124 

59. TraveUng Platform for the Excavation of the Upper Side of the 

Murray Hill Tunnel 125 

60. Timbering Used in the Murray Hill Tunnel 126 

61. Diagram Showing Sequence of Excavation in Heading Method of 

Tunneling Rock 132 



LIST OF ILLUSTRATIONS ix 

rXGUKB PAGE 

62. Method of Strutting Roof, St. Gothard Tunnel 135 

63. Sketch Showing Arrangement of Tracks, St. Gothard Tunnel 135 

64. Arrangement of Drill Holes in the Fort George Tunnel 137 

65. Longitudinal Section of the Heading and Bench Excavation at the 

Fort George Tunnel 137 

66. Diagram Showing the Arrangement of Drill Holes in the Heading 

and Bench of the GaUitsin Tunnel 140 

67. Diagram Showing Modification of the Heading and Bench Method 140 
68 and 68 A. Diagrams Showing Sequence of Excavation in the Belgian 

Method 145 

69. Sketch Showing Radial Roof Strutting, Belgian Method 147 

70. Sketch Showing Roof Arch Center, Belgian Method 147 

71. Sketch Showing Method of Underpinning Roof Arch with the Side 

Wall Masonry 149 

72. Longitudinal Section Showing Construction by the Belgian 

Method 149 

73. Diagram Showing Sequence of Excavation in Modified Belgian 

Method 152 

74. Sketch Showing Failure of Roof Arch by Opening at Crown 153 

75. Sketch Showing Methods of Repairing Roof Arch Failures 154 

76. Diagrams Showing Sequence of Excavation in German Method of 

Tunneling 155 

77. Diagram Showing Sequence of Excavation in Water Bearing 

Material, German Method 156 

78. Sketch Showing Work of Excavating and Timbering Drifts and 

Headings 157 

79. Sketch Showing Method of Roof Strutting 157 

80. Sketch Showing Roof Arch Centers and Arch Construction 158 

81. Sketch Showing Method of Excavating and Strutting Baltimore 

Belt Line Tunnel 162 

82. Roof Arch Construction with Timber Centers, Baltimore Belt Line 

Tunnel 163 

83. Roof Arch Construction with Iron Centers, Baltimore Belt Line 

Tunnel 164 

84. Diagram Showing Sequence of Excavation in English Method of 

Tunneling 167 

85. Sketches Showing Construction of Strutting, English Method 168 

86 and 87. Sketches of Typical Timber Roof- Arch Centers, English 

Method 169 



X LIST OF ILLUSTRATIONS 

FIGURE PAGE 

88. Sequence of Excavation in the American Method 172 

89. Strutting the Heading in the American Method 172 

90. Temporary Timbering of the Roof in the American Method 173 

91. Showing Crown Bars Supported by Segmental Arches 173 

92. Transversal and Longitudinal Section of a Tunnel Excavated and 

Strutted According to the American Method 174 

93 and 94. Diagrams Showing Sequence of Excavation in Austrian 

Method of Tunneling 177 

95, 96 and 97. Sketches Showing Construction of Strutting, Austrian 

Method 178 

98. Sketch Showing Manner of Constructing the Lining Masonry, 

Austrian Method 179 

99. Diagram Showing Sequence of Excavation in Italian Method of 

TunneUng 183 

100. Sketch Showing Strutting for Lower Part of Section 183 

101 and lOlA. Sketches Showing Construction of Centers, Italian 

Method 184 

102. Sketch Showing Invert and Foundation Masonry, Italian Method . 185 

103. Sketch Showing Longitudinal Section of a Tunnel under Construc- 

tion, Itahan Method 186 

104. Sketch Showing Sequence of Excavation, Stazza Tunnel 186 

105. Sketch Showing Method of Strutting First Drift, Stazza Tunnel 187 
106 and 107. Sketches Showing Temporary Strutting Arch Con- 
struction, Stazza Tunnel 187 

108. Sketch Showing Preliminary Drainage Galleries, Quicksand 

Method 190 

109. Sketch Showing Construction of Roof Strutting, Quicksand Method 190 

110. Sketch Showing Construction of Masonry Lining, Quicksand 

Method 191 

111. Sketch Showing Pilot Method of TunneUng 193 

112. Diagram Showing Sequence of Construction in Open-Cut Tunnels . 197 

113. Sketch Showing Method of Timbering Open-Cut Tunnels, Double 

Parallel Trench Method 198 

114. Side- Wall Foundation Construction Open-Cut Tunnels 198 

115. Wide-Arch Section, Boston Subway 204 

116. Double-Barrel Section, Boston Subway 205 

117. Four-Track Rectangular Section, Boston Subway 206 

118. Section Showing Slice Method of Construction, Boston Subway . . . 206 



LIST OF ILLUSTRATIONS XI 

FIGURE PAGE 

119. Double-Track Section, New York Rapid Transit Railway 212 

120. Park Avenue Deep Tunnel Construction, New York Rapid Transit 

Railway . . . 214 

121. Harlem River Tunnel, New York Rapid Transit Railway 215 

122. Sketch Showing Underground Stream, Milwaukee Water-Works 

Tunnel 229 

123. Sketch Showing Methods of Lining, Milwaukee Water- Works 

Tunnel 232 

124. Longitudinal Section of Brunei's Shield, First Thames Tunnel .... 241 

125. First Shield Invented by Barlow 242 

126. Second Shield Invented by Barlow 243. 

127. Shield Suggested by Greathead for the Proposed North and South 

Woolwich Subway 245 

128. Beach's Shield Used on Broadway Pneumatic Railway Tunnel .... 245 

129. Shield for City and South London Railway 246 

130.. Shield for St. Clair River Tunnel 247 

131. Shield for Blackwall Tunnel 248 

132. Elliptical Shield for Clichy Sewer Tunnel, Paris 249 

133. Semi-Elliptical Shield for Clichy Sewer Tunnel 250 

134. Roof Shield for Boston Subway 251 

135. Transversal and Longitudinal Section of Prelini's Shield 252 

136. Elevation and Section of Hydraulic Jack, East River Gas Tunnel. . 260 

137. Cast-iron Lining, St. Clair River Tunnel 262 

138. General Elevations and Sections of Shields 270 

139. Plan and Elevation of First Bulkhead Wall in South Tube, Man- 

hattan 273 

140. Typical Cross-Sections of One Tube of Pennsylvania Railroad 

Tunnel under the Hudson River 278 

141. Sections of Cofferdam, Van Buren St. Tunnel, Chicago 283 

142. Showing Working Platforms and Piles Sunk in Dredged Channel . . 286 

143. Showing Sheeting-Piles for the Sides of the Caisson and Trussed 

Beam for the Roof 287 

144. Showing the Caisson with the Working-Chamber 287 

145. Showing the Tunnel Constructed within the Caisson 289 

146. Showing Sides of the Caisson and Supports for the Roof 290 

147. Showing the Roof of the Caisson Formed by the Upper Half of the 

Tunnel : 291 

148. Showmg the Tunnel Completed by Building the Lower Half within 

the Caisson 292 



Xll LIST OF ILLUSTRATIONS 

FIGURE PAGH 

149. Transversal Section of the Caissons for the Tunnel under the Seine 

River 294 

150. Showing the Joining of the Caissons at the Pont Mirabeau Tunnel 

under the Seine River 295 

151. Cross-Sections and Plans of the Detroit River Tunnel 298 

152. Tunneling through Caved Material by Heading 306 

153. Tunneling through Caved Material by Drifts 307 

154 and 155. Filling in Roof Cavity Formed by FaUing Material 307 

156. Timbering to Prevent Landslides at Portal 308 

157. Shortening Tunnel Crushed by Landslide at Portal 308 

158. Extending Tunnel through Landshde at Portal 309 

159 and 160. Relining Timber-Lined Tunnel 316 

161. Relining Timber-Lined Tunnel, Great Northern Ry 317 

162. Relining Timber-Lined Tunnel, Great Northern Ry 318 

163. Relining Timber-Lined Tunnel, Great Northern Ry 319 

164. Construction of Centering MuUan Tunnel 320 

165. Centering Mullan Tunnel 321 

166. Relining Timber-Lined Tunnel, Norfolk & Western Ry 322 

167. Relining Timber-Lined Tunnel, Norfolk & Western Ry 323 



IlSTTRODL^OTIOIf 



THE HISTORICAL DEVELOPMENT OF TUNNEL 

BUILDING. 

A TUNNEL, defined as an engineering structure, is an artificial 
gallery, passage, or roadway beneath the ground, under the bed 
of a stream, or through a hill or mountain. The art of tunnel- 
ing has been known to man smce very ancient times. A The- 
ban king on ascending the throne began at once to drive the 
long, narrow passage or tunnel leading to the inner chamber or 
sepulcher of the rock-cut tomb which was to form his final 
resting-place. Some of these rock-cut galleries of the ancient 
Egyptian kings were over 750 ft. long. Similar rock-cut tun- 
neling work was performed by the Nubians and Indians in 
building their temples, by the Aztecs in America, and in fact 
by most of the ancient civilized peoples. 

The first built-up tunnels of which there are any existing 
records were those constructed by the Assyrians. The vaulted 
drain or passage under the southeast palace of Nimrud, built by 
Shalmaneser II. (860-824 B.C.), is in all essentials a true soft- 
ground tunnel, with a masonry lining. A much better exam- 
ple, however, is the tunnel under the Euphrates River, which 
may quite accurately be claimed as the first submarine turaiel 
of which there exists any record. It was, however, built under 
the dry bed of the river, the waters of which were temporarily 
diverted, and then turned back into their normal channel aiter 
the tunnel work was completed, thus making it a true sub- 
marine tunnel only w^hen finished. The Euphrates River tun- 
nel was built through soft ground, and was lined with brick 

xiii 



XIV INTRODUCTION 

masonry, having interior dimensions of 12 ft. in widtli and 15 
ft. in height. 

Only hand labor was employed by these ancient peoples in 
their tunnel work. In soft ground the tools used were the 
pick and shovels, or scoops. For rock work they possessed a 
greater range of appliances. Research has shown that among 
the Egyptians, by whom the art of quarrying was highly de- 
veloped, use was made of tube drills and saws provided with 
cutting edges of corundum or other hard, gritty material. The 
usual tools for rock work were, however, the hammer, the chisel, 
and wedges ; and the excellence and magnitude of the works 
accomplished by these limited appliances attest the imlimited 
time and labor which must have been available for their ac- 
complishment. 

The Romans should doubtless rank as the greatest tunnel 
builders of antiquity, in the number, magnitude, and useful 
character of their works, and in the improvements which they 
devised in the methods of tunnel building. They introduced 
fire as an agent for hastening the breaking down of the rock, 
and also developed the familiar principle of prosecuting the 
work at several points at once by means of shafts. In their 
use of fire the Romans simply took practical advantage of the 
familiar fact that when a heated rock is suddenly cooled it 
cracks and breaks so that its excavation becomes comparatively 
easy. Their method of operation was simply to build large 
fires in front of the rock to be broken down, and when it had 
reached a high temperature to cool it suddenly by throwing 
water upon the hot surface. The Romans were also aware 
that vinegar affected calcareous rock, and in excavating tunnels 
through this material it was a common practice with them to 
substitute vinegar for water as the coohng agent, and thus to 
attack the rock both chemically and mechanicalljr. It is hardly 
necessary to say that this method of excavation was very severe 
on the workmen because of the heat and foul gases generated. 
This was, however, a matter of small concern to the builders, 



INTRODUCTION XV 

since the work was usually performed by slaves and prisoners 
of war, who perished by thousands. To be sentenced to labor 
on Roman tunnel works was thus one of the severest penalties 
to which a slave or prisoner could be condemned. They were 
places of suffering and death as are to-day the Spanish mercury 
mines. 

Besides their use of fire as an excavating agent, the Romans 
possessed a very perfect knowledge of the use of vertical shafts 
in order to prosecute the excavation at several different points 
simultaneously. Pliny is authority * for the statement that in 
the excavation of the tunnel for the drainage of Lake Fucino 
forty shafts and a number of inclined galleries were sunk along 
its length of 3^ miles, some of the shafts being 400 ft. in 
depth. The spoil was hoisted out of these shafts in copper 
pails of about ten gallons' capacity by windlasses. 

The Roman tunnels were designed for public utility. Among 
those which are most notable in this respect, as well as for 
being fine examples of tunnel work, may be mentioned the nu- 
merous conduits driven through the calcareous rock between 
Subiaco and Tivoli to carry to Rome the pure water from the 
mountains above Subiaco. This work was done under the 
Consul Marcius. The longest of the Roman tunnels is the one 
built to drain Lake Fucino, as mentioned above. This tunnel 
was designed to have a section of 6 ft. x 10 ft. ; but its actual 
dimensions are not uniform. It was driven through calcareous 
rock, and it is stated that 30,000 men were employed for eleven 
years in its construction. The tunnels which have been men- 
tioned, being designed for conduits, were of small section ; but 
the Romans also built tunnels of larger sections at numerous 
points along their magnificent roads. One of the most notable 
of these is that which gives the road between Naples and Poz- 
zuoli passage through the Posilipo hills. It is excavated 
through volcanic tufa, and is about 3000 ft. long and 25 ft. 
wide, with a section of the form of a pointed arch. In order 

* "Tunneling," Encly. Brit., 1889, vol. xxiii., p. 623. 



XVI INTRODUCTION 

to facilitate the illumination of this tunnel, its floor and roof 
were made gradually converging from the ends toward the 
middle ; at the entrances the section was 75 ft. high, while at 
the center it was only 22 ft. high. This double funnel-like 
construction caused the rays of light entering the tunnel to 
concentrate as they approached the center, and thus to improve 
the natural illumination. The tunnel is on a grade. It was 
probably excavated during the time of Augustus, although 
some authorities place its construction at an earlier date. 

During the Middle Ages the art of tunnel building was 
practiced for military purposes, but seldom for the public need 
and comfort. Mention is made of the fact that in 1450 Anne 
of Lusignan commenced the construction of a road tunnel 
under the Col di Tenda in the Piedmontese Alps to afford 
better communication between Nice and Genoa ; but on account 
of its many difficulties the work was never completed, although 
it was several times abandoned and resumed. For the most 
part, therefore, the tunnel work of the Middle Ages was in- 
tended for the purposes and necessities of war. Every castle 
had its private underground passage from the central tower or 
keep to some distant concealed place to permit the escape of 
the family and its retainers in case of the victory of the enemy, 
and, during the defense, to allow of sorties and the entrance 
of supplies. 

The tunnel builders of the Middle Ages added little to the 
knowledge of their art. Indeed, until the 17th century and 
the invention of gunpowder no practical improvement was 
made in the tunneling methods of the Romans. Engravings 
of mining operations in that century show that underground 
excavation was accomplished by the pick or the hammer and 
chisel, and that wood fires were lighted at the ends of the 
headings to split and soften the rocks in advance. Although 
gunpowder had been previously employed in mining, the first 
important use of it in tunnel work was at Malpas, France, 
in 1679-81, in the tunnel for the Languedoc Canal. This 



INTRODUCTION XVll 

tunnel was 510 ft. long, 22 ft. wide, and 29 ft. high, and was 
excavated through tufa. It was left unlined for seven years, 
and then was lined with masonry. 

With the advent of gunpowder and canal building the lirst 
strong impetus was given to tunnel building, in its modern 
sense, as a commercial and public utilitarian construction, since 
the days of the Roman Empire. Canal tunnels of notable 
size were excavated in France and England during the last 
half of the 17th century. These were all rock or hard-ground 
tunnels. Indeed, previous to 1800 the soft-ground tunnel was 
beyond the courage of engineer except in sections of such 
small size that the work better deserves to be called a drift or 
heading than a tunnel. In 1803, however, a tunnel 24 ft. 
wide was excavated through soft soil for the St. Quentin Canal 
in France. Timbering or strutting was employed to support 
the walls and roof of the excavation as fast as the earth was 
removed, and the masonry lining was built closely following it. 
From the experience gained in this tunnel were developed the 
various systems of soft-ground subterrannean tunneling since 
employed. 

It was by the development of the steam railway, however, 
that the art of tunneling was to be brought into its present 
prominence. In 1820-26 two tunnels were built on the Liver- 
pool & Manchester Ry. in England. This was the beginning 
of the rapid development which has made the tunnel one of 
the most familiar of engineering structures. The first railway 
tunnel in the United States was built on the Alleghany & 
Portage R.R. in Pennsylvania in 1831-33 ; and the first canal 
tunnel had been completed about 13 years previously (1818-21) 
by the Schuylkill Navigation Co., near Auburn, Pa. It would 
be interesting and instructive in many respects to follow the 
rise and progress of tunnel construction in detail since the con- 
struction of these earlier examples, but all that may be said 
here is that it was identical with that of the railway. 

The art of tunneling entered its last and greatest phase 



^vm INTKODUCTION 

with the construction of the Mont Cenis tunnel in Europe and 
the Hoosac tunnel in America, which works established the 
utility of machine rock-drills and high explosives. The Mont 
Cenis tunnel was built to facilitate railway communication 
between Italy and France, or more properly between Pied- 
mont and Savoy, the two parts of the kingdom of Victor 
Emmanuel II., separated by the Alps. It is 7.6 miles long, 
and passes under the Col di Frejus near Mont Cenis. Som- 
meiller, Grattoni, and Grandis were the engineers of this great 
undertaking, which was begun in 1857, and finished in 1872. 
It was from the close study of the various difficulties, the great 
length of the tunnel, and the desire of the engineers to finish 
it quickly, that all the different improvements were developed 
which marked this work as a notable step in the advance of 
the art of tunneling. Thus the first power-drill ever used in 
tunnel work was devised by Sommeiller. In addition, com- 
pressed air as a motive power for drills, aspirators to suck the 
foul air from the excavation, air compressors, turbines, etc., 
found at Mont Cenis their first application to tunnel construc- 
tion. This important role played by the Mont Cenis tunnel 
in Europe in introducing modern methods had its counterpart 
in America in the Hoosac tunnel completed in 1875. In this 
work there were used for the first time in America power rock- 
drills, air compressors, nitro-glycerine, electricity for firing 
blasts, etc. 

There remains now to be noted only the final development 
in the art of soft-ground submarine tunneling, namely, the use 
of the shield and metal lining. The shield was invented and 
first used by Sir Isambard Brunei in excavating the tunnel 
under the River Thames at London, which was begun in 1825, 
and finished in 1841. In 1869 Peter William Barlow used an 
iron lining in connection with a shield in driving the second 
tunnel under the Thames at London. From these inventions 
has grown up one of the most notable systems of tunneling 
now practiced, which is commonly known as the shield system. 



INTRODUCTION XIX 

In closing this brief review of the development of modern 
.methods of tunneling, to the presentation of which the re- 
mainder of this book is devoted, mention should be made of 
a form of motive power which promises many opportunities for 
development in tunnel construction. Electricity has long been 
employed for blasting and illuminating purposes in tunnel 
work. It remains to be extended to other uses. For hauling 
and for operating certain classes of hoisting and excavating 
machinery it is one of the most convenient forms of power 
available to the engineer. Its successful application to rock- 
drills is another promising field. For operating ventilating 
fans it promises unusual usefulness. 



TUNNELING 



CHAPTER I. 

PRELIMINARY CONSIDERATIONS. CHOICE BE- 

TWEEN A TUNNEL AND OPEN CUT. 

GEOLOGICAL SURVEYS. 



CHOICE BETWEEN A TUNNEL AND AN OPEN CUT. 

When a railway line is to be carried across a range of 
mountains or hills, the first question which arises is whether 
it is better to construct a tunnel or to make such a detour as 
will enable the obstruction to be passed with ordinary surface 
construction. The answer to this question depends upon the 
comparative cost of construction and maintenance, and upon 
the relative commercial and structural advantages and disad- 
vantages of the two methods. In favor of the open road there 
are its smaller cost and the decreased time required in its con- 
struction. These mean that less capital will be required, and 
that the road will sooner be able to earn something for its 
builders. Against the open road there are : its greater length 
and consequently its heavier running expenses; the greater 
amount of rolling-stock required to operate it ; the heavy ex- 
pense of maintaining a mountain road; and the necessity of 
employing larger locomotives, with the increased expenses which 
they entail. In favor of the tunnel there are : the shortening 
of the road, with the consequent decrease in the operating 
expenses and amount of rolling-stock required ; the smaller cost 



Z TUNNELING 

of maintenance, owing to the protection of the track from snow 
and rain and other natural influences causing deterioration ; 
and the decreased cost of hauling due to the lighter grades. 
Against the tunnel, there are its enormous cost as compared 
with an open road and the great length of time required to 
construct it. 

To determine in any particular case whether a tunnel or an 
open road is best, requires a careful integration of all the factors 
mentioned. It may be asserted in a general way, however, that 
the enormous advance made in the art of tunnel building has 
done much to lessen the strength of the principal objections to 
tunnels, namely, their great cost and the length of time required 
for their construction. Where the choice lies between a tunnel 
or a long detour with heavy grades it is sooner or later almost 
always decided in favor of a tunnel. When, however, the con- 
ditions are such that the choice lies between a tunnel or a 
heavy open cut with the same grades the problem of deciding 
between the two solutions is a more difficult one. 

It is generally assumed that when the cut required will have 
a vertical depth exceeding 60 ft. it is less expensive to build 
a tunnel unless the excavated material is needed for a nearby 
embankment or fill. This rule is not absolute, but varies 
according to local conditions. For instance, in materials of 
rigid and unyielding character, such as rock, the practical hmit 
to the depth of a cut goes far beyond that point at which a 
tunnel would be more economical according to the above rule. 
In soils of a yielding character, on the other hand, the very 
flat slope required for stability adds greatly to the cost of 
making a cut. 

It may be noted in closing that the same rule may be em- 
ployed in determining the location of the ends of the tunnel, 
for assuming that it is more convenient to excavate a tun- 
nel than an open cut when the depth exceeds 60 ft., then 
the open cut approaches should extend into the mountain- or 
hill-sides only to the points where the surface is 60 ft. above 



CHOICE BETWEEN A TUNNEL AND AN OPEN CUT S 

grade, and there the tunnel should begin. If, therefore, we 
draw on the longitudinal profile of the tunnel a line parallel to 
the plane of the tracks, and 60 ft. above it, this line will cut 
the surface at the points where the open-cut approaches should 
cease and the tunnel begin. This is a rule-of-thumb determi- 
nation at the best, and requires judgment in its use. Should 
the ground surface, for example, rise only a few feet above the 
60 ft. line for any distance, it is obviously better to continue 
the open cut than to tunnel. 

THE METHOD AND PURPOSE OF GEOLOGICAL SURVEYS. 

When it has been decided to build a tunnel, the first duty 
of the engineer is to make an accurate geological survey of 
the locality. From this survey the material penetrated, the 
form of section and kind of strutting to be used, the best form 
of lining to be adopted, the cost of excavation, and various 
other facts, are to be deduced. In small tunnels the geological 
knowledge of the engineer should enable him to construct a 
geological map of the locality, or this knowledge may be had 
in many cases by consulting the geological maps issued by the 
State or general government surveys. When, however, the 
tunnel is to be of great length, it may be necessary to call in 
the assistance of a professional geologist in order to reconstruct 
accurately the interior of the mountain and thereby to ascer- 
tain beforehand the different strata and materials to be 
excavated, thus obtaining the data for calculating both the 
time and cost of excavating the tunnel. 

The geological survey should enable the engineer to deter- 
mine, (1) the character of the material and its force of cohe- 
sion, (2) the inclination of the different strata, and (3) the 
presence of water. 

Character of Material. — The character of the material through 
which the proposed tunnel will penetrate is best ascertained 
by means of diamond rock-drills. These machines bore an 



4 TUNNELING 

annular hole, and take away a core for the whole depth of the 
boring, thus giving a perfect geological section showing the 
character, succession, and exact thickness of the strata. By 
making such borings at different points along the center line 
of the projected tunnel, and comparing the relative sequence 
and thickness of the different strata shown by the cores, the 
geological formation of the mountain may be determined quite 
exactly. Where it is difficult or impracticable to make dia- 
mond drill borings on account of the depth of the mountain 
above the tunnel, or because of its inaccessibility, the engineer 
must resort to other methods of observation. 

The present forms of mountains or hills are due to 
weathering, or the action of the destructive atmospheric influ- 
ences upon the original material. From the manner in which 
the mountain or hill has resisted weathering, therefore, may be 
deduced in a general way both the nature and consistency of 
the materials of which it is composed. Thus we shall gener- 
ally find mountains or hills of rounded outlines to consist 
of soft rocks or loose soils, while under very steep and crested 
mountains hard rock usually exists. To the general knowl- 
edge of the nature of its interior thus afforded by the ex- 
terior form of the mountain, the engineer must add such 
information as the surface outcroppings and other local evi- 
dences permit. 

For the purposes of the tunnel builder we may first classify 
all materials as either, (1) hard rock, (2) soft rock, or (3) 
soft soil. 

Hard rocks are those having sufficient cohesion to stand 
vertically when cut to any depth. Many of the primary rocks, 
like granite, gneiss, feldspar, and basalt, belong to this class, 
but others of the same group are affected by the atmosphere, 
moisture, and frost, which gradually disintegrate them. They 
are also often found interspersed with pyrites, whose well- 
known tendency to disintegrate upon exposure to air intro- 
duces another destructive agency. For these reasons we may 



CHOICE BETWEEN A TUNNEL AND AN OPEN CUT 6 

divide hard rocks into two sub-classes ; viz., hard rocks un- 
affected by the atmosphere, and those affected by it. This 
distinction is chiefly important in tunneling as determining 
whether or not a lining will be required. 

Soft rocks, as the term implies, are those in which the force 
of cohesion is less than in hard rocks, and which in consequence 
offer less resistance to attacks tending to break down their 
original structure. They are always affected by the atmosphere. 
Sandstones, laminated clay shales, mica-schists, and all schistose 
stones, chalk and some volcanic rocks, can be classified in this 
group. Soft rocks require to be supported by timbering during 
excavation, and need to be protected by a strong lining to 
exclude the air, and to support the vertical pressures, and 
prevent the fall of fragments. 

Soft soils are composed of detrital materials, having so little 
cohesion that they may be excavated without the use of 
explosives. Tunnels excavated through these soils must be 
strongly timbered during excavation to support the verti- 
cal pressure and prevent caving ; and they also always require 
a strong lining. Gravel, sand, shale, clay, quicksand, and peat 
are the soft soils generally encountered in the excavation of 
tunnels. Gravels and dry sand are the strongest and firmest ; 
shales are very firm, but they possess the great defect of being 
liable to swell in the presence of water or merely by exposure 
to the air, to such an extent that they have been known to 
crush the timbering built to support them. Quicksand and 
peat are proverbially treacherous materials. Clays are some- 
times firm and tenacious, but when laminated and in the 
presence of water are among the most treacherous soils. 
Laminated clays may be described as ordinary clays altered 
by chemical and mechanical agencies, and several modifications 
of the same structure are often found in the same locality. 
They are composed of laminae of lenticular form separated by 
smooth surfaces and easily detached from each other. Lami- 
nated clays generally have a dark color, red, ocher or greenish 



6 TUNNELING 

blue, and are very often found alternating with strata of 
stiatites or calcareous material. For purposes of construction 
they have been divided into three varieties. 

Laminated clays of the first variety are those which alter- 
nate with calcareous strata and are not so greatly altered as 
to lose their original stratification. Laminated clays of the 
second variety are those in which the calcareous strata are 
broken and reduced to small pieces, but in which the former 
structure is not completely destroyed ; the clay is not reduced 
to a humid state. Laminated clays of the third variety 
are those in which the clay by the force of continued disturb- 
ance, and in the presence of water, has become plastic. 
Laminated clays are very treacherous soils ; quicksand and 
peat may be classed, as regards their treacherous nature, 
among the laminated clays of the third variety. 

Inclination of Strata Knowing the inclination of the 

strata, or the angle which they make with the horizon, it is 
easy to determine where they intersect the vertical plane of the 
tunnel passing through the center line, thus giving to a certain 
extent a knowledge of the different strata which will be met 
in the excavatioUo On the inclination of the strata depend : 
(1) The cost of the excavation ; the blasting, for instance, will 
be more efficient if the rocks are attacked perpendicular to the 
stratification; (2) The character of the timbering or strut- 
ting ; the tendency of the rock to fall is greater if the strata 
are horizontal than if they are vertical ; (3) The character and 
thickness of the lining; horizontal strata are in the weakest 
position to resist the vertical pressure from the load above 
when deprived of the supporting rock below, while vertical 
strata, when penetrated, act as a sort of arch to support the 
pressure of the load above. The foregoing remarks apply 
only to hard or soft rock materials. 

In detrital formations the inclination of the strata is an 
important consideration, because of the unsymmetrical pres- 
sures developed. In excavating a tunnel through soft soil 



CHOICE BETWEEN A TUN:NEL AND AN OPEN CUT i 

whose strata are inclined at 30° to the horizon, for instance, 
the tunnel will cut these strata at an angle of 30°. By the 
excavation the natural equilibrium of the soil is disturbed, 
and while the earth tends to fall and settle on both sides 
at an angle depending upon the friction and cohesion of the 
material, this angle will be much greater on one side than on 
the other because of the inclination of the strata; and hence 
the prism of falling earth on one side is greater than on the 
other, and consequently the pressures are different, or irt 
other words, they are unsymmetrical. These unsymmetricaL 
pressures are usually easily taken care of as far as the lining 
is concerned, but they may cause serious cave-ins and badljr 
distort the strutting. Caving-in during excavation may be; 
prevented by cutting the materials according to their natural, 
slope; but the distortion of the strutting is a more serious 
problem to handle, and one which oftentimes requires the 
utmost vigilance and care to prevent serious trouble. 

Presence of Water. — An idea of the likelihood of finding 
water in the tunnel may be obtained by studying the hydro- 
graphic basin of the locality. From it the source and direction 
of the springs, creeks, ravines, etc., can be traced, and from 
the geological map it can be seen where the strata bearing 
these waters meet the center line. Not only ought the surface 
water to be attentively studied, but underground springs, which 
are frequently encountered in the excavation of tunnels, re- 
quire careful attention. Both the surface and underground 
waters follow the pervious strata, and are diverted by im- 
pervious strata. Rocks generally may be classed as im- 
pervious ; but they contain crevices and faults, which often, 
allow water to pass tlirough them ; and it is, therefore, not 
uncommon to encounter large quantities of water in excavating 
tunnels through rock. As a rule, water will be found under 
high mountains, which comes from the melted ice and snow 
percolating through the rock crevices. 

Some detiital soils, like gravel and sand, are pervious, and 



8 TUNNELING 

others, like clay and shale, are impervious. Detrital soils 
lying above clay are almost certain to carry water just above 
the clay stratum. In tunnel work, therefore, when the exca- 
vation keeps well within the clay stratum, little trouble is 
likely to be had from water ; should, however, the excavation 
cut the clay surface and enter the pervious material above, 
water is quite certain to be encountered. The quantity of 
water encountered in any case depends upon the presence of 
high mountains near by, and upon other circumstances which 
will attract the attention of the engineer. 

A knowledge of the pressure of the water is desirable. 
This may be obtained by observing closely its source and the 
character of the strata through which it passes. Water 
coming to the excavation through rock crevices will lose 
little of its pressure by friction, while that which has passed 
some distance through sand will have lost a great deal of its 
pressure by friction. Water bearing sand, and, in fact, any 
water bearing detrital material, has its fluidity increased by 
water pressure ; and when this reaches the point where flow 
results, trouble ensues. The streams of water met in the 
construction of the St. Gothard tunnel had sufficient pressure 
to carry away timber and materials. 



DETERMINING THE CENTER LINE 



CHAPTER 11. 

METHODS OF DETERMINING THE CENTER 

LINE AND FORMS AND DIMENSIONS OF 

CROSS-SECTION. 



DETERMINING THE CENTER LINE. 

Tunnels may be either curvilinear or rectilinear, but the 
latter form is the more common. In either case the first task 
of the engineer, after the ends of the tunnel have been definitely 
fixed, is to locate the center line exactly. This is done on the 
surface of the ground; and its purpose is to find the exact 
length of the tunnel, and to furnish a reference line by which 
the excavation is directed. 

Rectilinear Tunnels. — In short tunnels the center line may be 
accurately enough located for all practical purposes by means 
of a common theodolite. The work is performed on a calm, 
clear day, so as to have the instrument and observations sub- 
jected to as little atmospheric disturbance as possible. Wooden 
stakes are employed to mark the various located points of the 
center line temporarily. The observations are usually repeated 
once at least to check the errors, and the stakes are altered as 
the corrections dictate ; and after the line is finally decided to 
be correctly fixed, they are replaced by permanent monu- 
ments of stone accurately marked. The method of checking the 
observations is described by Mr. W. D. HaskoU * as follows : 

"Let the theodolite be carefully set up over one of the stakes, with the 
nail driven into it, selecting one that will command the best position so as to 
range backwards and forwards over the whole length of line, and also obtain a 
view of the two distant points that range with the center line ; this being done, 

* " Practical Tunneling," by F. W. Simms. 



10 TUNNELING 

let the centers of every stake ... be carefully verified. If this be carefully 
done, and the centers be found correct, and thoroughly in one visual line as 
seen through the telescope, there will be no fear but that a perfectly straight 
line has been obtained. 

The center line which has thus been located on the ground 
surface has to be transposed to the inside of the tunnel to 
direct the excavation. To do this let A and B be the entrances 
and a and b be the two distinct fixed points which have been 
ranged in with the center line located on the ground surface 
over the hill AfB, Fig. 1. The instrument is set up at V, 
any point on the line A a produced, and a bearing secured by 
observation on the center line marked on the surface. This 
bearing is then carried into the tunnel by plunging the tele- 
scope, and setting pegs in the roof of the heading. Lamps 



B A V 

Fig. 1. — Diagram Showing Manner of Lining in Rectilinear Tunnels. 

hung from these pegs furnish the necessary sighting points. 
This same operation is repeated on the opposite side of the 
hill to direct the excavation from that end of the tunnel. 
These operations serve to locate only the first few points inside 
the tunnel. As the excavation penetrates farther into the hill, 
it becomes impossible to continue to locate the line from the 
outside point, and the line has to be run from the points 
marked on the roof of the heading. Great accuracy is required 
in all these observations, since a very small error at the begin- 
ning becomes greater and greater as the excavation advances. 
To facilitate the accurate location of points on the roof of the 
tunnel, a simple device was designed by Mr. Beverley R. Value, 
shown in Fig. 2. Two iron spikes, each having a small hole 
in the flat end, are driven into the rock about 9 ins. apart. A 
brass bar, 1 in. high, I in. thick and 10 ins. long, having a hole 
near one end and a 1 in. slot at the other, is screwed tightly into 



DETERMINING THE CENTER LINE 



11 




|MM|iiii|(Hi|iiii|iin|Mn(in|prTTjtfffjlTTT) 



¥ 




Fig. 2. — B. R. Value's Device for Locating 
the Center Line Inside of a Tunnel. 



the head of the spikes. The middle part of the bar is divided 
into inches and tenths of an inch. A separate brass hanger is 
fitted to the bar, having a vernier with its zero at the middle 
of the hanger and corre- 
sponding to a plumb line at- 
tached below. The hanger 
is moved back and forth until 
it coincides with the line of 
sight of the transit, and then 
the readings of the vernier 
are recorded. Any time that 
the hanger is placed on the 
bar and the vernier marks 
the same reading, the plumb 
line will indicate the center 
line of the tunnel. When, 

instead of one bar, two are inserted at a distance of 20 or 30 ft. 
apart, the plumb lines suspended from the hangers will repre- 
sent the vertical plane passing through the axis of the tunnel 
in coincidence with the one staked out on the surface ground. 

The location of the center line of a long tunnel, which is to be 
excavated under high mountains, is a very difficult operation, 
and the engineers usually leave this part of the work to astrono- 
mers, who fix the stations from which the engineers direct the 
work of construction. The center lines of all the great Alpine 
tunnels were located by astronomers who used instruments 
of large size. Thus, in ranging the center line of the St. Gothard 
tunnel, the theodolite used had an object glass eight inches 
in diameter.* Instead of the ordinary mounting a masonry 
pedestal with a perfectly level top is employed to support the 
instrument during the observations. The location is made by 
means of triangulation. The various operations must be per- 
formed with the greatest accuracy, and repeated several times 
in such a way as to reduce the errors to a minimum, since 

* See also the Simplon Tunnel, Chapter IX. 



12 



TUNNELING 



the final meeting of the headings depends upon their eHmi- 
nation. 

The St. Gothard tunnel furnishes perhaps the best illustra- 
tion of careful work in locating the center line of long recti- 
hnear tunnels of any tunnel ever built. The length of this 
tunnel is 9.25 miles, and the height of the mountain above it 
is very great. The center line was located by triangulation by 
two different astronomers using different sets of triangles, and 
working at different times. The set or system of triangles used 
by Dr. Koppe, one of the observers, is shown by Fig. 3; it con- 
sists of very large and quite small triangles combined, the latter 
being required because the entrances both at Airolo and Goes- 



VBoreh 



Vl.Stabbielh 




mfibbla 
Fig. 3. — Triangulation System for Establishing the Center Line of the St. Gothard Tunnel. 

chenen were so low as to permit only of a short sight being 
taken. The apices of the triangles were located by means 
of the contour maps of the Swiss Alpine Club. Each angle 
was read ten times, the instrument was colhmated four times 
for each reading, and was afterwards turned off 5° or 10° to 
avoid errors of graduation. The average of the errors in read- 
ing was about one second of arc. The triangulation was compen- 
sated according to the method of least squares. The probable 
error in the fixed direction was calculated to be 0.8'' of arc at 
Goeschenen and 0.7'' of arc at Airolo. From this it was as- 
sumed that the probable deviation from the true center would 
be about two inches at the middle of the tunnel, but when the 



DETERMINING THE CENTER LINE 



13 



headings finally met this deviation was found to reach eleven 
inches. 

Comparatively few tunnels are driven by working from the 
entrances alone, the excavation being usually prosecuted at 
several points at once by means of shafts. In these cases, in 
order to direct the excavation correctly, it is necessary to fix the 
center fine on the bottom of the shaft. This is accomphshed in 
two ways, — one being employed when the shaft is located directly 
over the center line, and the other when the shaft is located to 
one side of the center line. 

When the shaft is located on the center line two small pillars 
are placed on opposite edges of the shaft and collimating with 
the center line as shown by Fig. 4. On these two pillars the 
points corresponding to the center line are correctly marked, 
and connected by a wire stretched between them. To this wire 
two plumb bobs are fastened as far apart as possible. These 
plumb bobs mark two points on the center fine at the bottom of 
the shaft, and from them the line is extended into the headings as 
the work advances. In these op- 
erations, heavy plumb bobs are 
used. In the New York subway 
plumb bobs of steel, weighing 25 
lbs. each, w^ere used, and to pre- 
vent rotation they were made with 
cross-sections, in the shape of a 
Greek cross, and were sunk in 
buckets filled with water. Owing 
to the difference between the tem- 
perature at the top and that at the 
bottom of the shaft, strong currents 
of air are produced, which keep in 
constant oscillation the wires to 
which the bobs are suspended. 

To determine the center line at the bottom of the shaft, the 
headings are first driven from both sides of the shaft, after which 



Wire 




Fig. 4. — Method of Transferring the 
Center Line down Center Shafts. 



ra 



14 TUNNELING 

a transit is set up on the same alignment with the two wires, 
and this will indicate the vertical plane passing through the 
axis of construction. Two points are then fixed on the roof 
of the tunnel in continuation of this vertical plane. When the 
plumb bobs are removed from the shaft and two small plumb 
bobs are suspended to the two points mentioned, they will 
always give the same vertical plane passing through the axis 
of construction transferred from the surface. 

Because of the continuous moving of the wires, the fixing of 
the points on the roof of the tunnel is very troublesome, and 
the operation should be repeated by different men at different 
times before the points are permanently fixed. 

When the shaft is placed at one side of the tunnel the pillars 

or bench marks are placed nor- 
mal to the center line on the 
edges of the shaft as shown by 
Tb Fig. 5. Between the points A 

I and B a wire is stretched, and 

J from it two plumb bobs are 

j^ suspended, as described in the 

: preceding case; these plumb 

Center |0 L/ne j^^j^g establish a vertical plane 

!^ normal to the axis of the tunnel. 

Fig. 5. - Method of Transferring the Center 'pj^g eXCaVatloU of the side tUU- 
Line down Side Shafts. 

nel is carried along the line BW 
until it intersects the line of the main tunnel, whose center line 
is determined by measuring off underground a distance equal 
to the distance BO on the surface. By setting the instrument 
over the underground point 0, and turning off a right angle 
from the fine BO, the center line of the tunnel is extended into 
the headings. 

Curvilinear Tunnels. — There are various methods of locating 
the center lines of curvilinear tunnels, but the method of tan- 
gent offsets is the one most commonly employed. 

At the beginning the excavation is conducted as closely as 



DETERMINING THE CENTER LINE 



15 



may be to the line of the curve, and as soon as it has progressed 
far enough the tangent AT, Fig. 6, is ranged out. At 5 a point 
is located over which to set the instrument, and the distance 
AB is measured for the purpose of finding the ordinate of 
the right angle triangle OAB. Now OA = r, AB = d, and = 



angle ABO. Then 



Tang. = - 



DoubUng the value of ^ and making the angle ABC =2 0, 
the line BC will be fixed and the point C located by taking 
AB = BC. On BC the ordinates are laid off to locate the curve. 
Prolong CB so that CD = CB. Then the portion of the curve 
CF is symmetrical with CE, and the ordinates used to locate 
EC may be employed to locate CF, by laying them off in the 
reverse order. 

In curvilinear tun- 
nels several cases may 
be considered. 

(1) When the tunnel 
for almost its entire 
length is driven on a 
tangent with a curve 
at each end. 

(2) When the tun- 
nel begins with a curve 
and ends with a straight 
line. 

(3) When the whole 
tunnel is in curve from portal to portal. 

(4) The helicoidal or corkscrew tunnel. 




Fig. 



Method of Laying Out the Center Line of 
Curvilinear Tunnels. 



(1) The axis of every one of the great Alpine tunnels is a 
straight line, with a curve at each end. To range out the center 
line of one of these long tunnels from a curve, no matter how 
accurately laid out, will certainly cause an error, which, magnified 
with the distance, may produce serious results. To avoid these 



16 TUNNELING 

inconveniences, the determination of the axis of the tunnel 
should be made from a straight Hne. This means that the tunnel 
is at first excavated on a straight line for its entire length and 
after the headings driven from both portals have met, the two 
portions of the tunnel or curve are excavated and constructed. 
The portions of the tunnel excavated on straight lines for con- 
veniences of construction may then be abandoned or used in 
cases of accidents or repairs. 

When the axis of a short tunnel has a curve at each end and 
a straight line in the middle, it is driven directly from the en- 
trances; first, however, excavating the curvihnear portions of 
the tunnel. In such a case it would be advisable to proceed 
in the following manner. Drive the headings on the curvilinear 
portions of the tunnel, staking out the center line by means of 
the offsets from the tangents. At the ends of the curves lay 
out from both fronts the rectilineal portion of the tunnel. Only 
very narrow headings should be excavated at first while the 
whole section could be enlarged near the entrances. The exca- 
vation of the headings at the front should advance very rapidly, 
in order that the headings may meet in the shortest possible time. 
When communication is established, it is comparatively easy to 
correct an error resulting from driving the tunnel from the curves. 

(2) When a tunnel begins with a curve and ends with a 
straight line, the work of excavation should proceed from both 
ends. From the straight end of the tunnel only the heading 
should be driven, while from the curvilinear end the whole 
section could be opened at once. By this arrangement the 
excavation progresses slowly from the curvilinear end and 
rapidly from the straight end of the tunnel. Once communica- 
tion has been established and any error corrected, the work of 
enlarging the profile of the tunnel may be pushed with the same 
activity from both ends. 

(3) When the center hne of the entire tunnel is a curve^ 
there is more probability of slight deviations from the true axis 
of the proposed work. In such a case it would be advisable to 



DETERMINING THE CENTER LINE 17 

first excavate a narrow heading and to concentrate all the efforts 
in driving the headings as rapidly as possible in order that they 
may meet in the shortest time. The center line of these headings 
is staked out by the usual method of the offsets from the tangent. 
The enlarging of the section of the tunnel could be commenced 
at both portals and be driven slowly until the headings have 
met and any errors corrected, w^hen the work could be pushed 
with the greatest activity all along the line. 

(4) In corkscrew or helicoidal tunnels the entire center line 
is on a curve. In these tunnels, as a rule, there is a great dif- 
ference of level between the two portals, one being much higher 
than the other, so careful attention should be paid to the tunnel 
grade. Working in the limited spaces afforded by narrow head- 
ings it is very probable that errors may be made in fixing both 
the alignment and the grade of the tunnel. To prevent these 
almost unavoidable errors, it would be well to excavate at first 
only the headings, to stake the center fine in the roof of these 
headings and then to lay the grade of the tunnel as accurately 
as possible. The work on the headings should be pushed as 
rapidly as possible in order that they may meet quickly, so that 
the center line, as temporarily laid out, may be corrected and 
permanently fixed for the direction of successive operations. 
In these tunnels the headings should be excavated near the 
center of the tunnel cross-section so that the sides and roof of 
the heading would be at some distance from the sides and roof 
of the proposed tunnel. This arrangement will easily permit 
corrections to be made in case any shght difference from the 
true line was erroneously made during the excavation of the 
headings. 

FORM AND DIMENSIONS OF CROSS-SECTION. 

In deciding upon the sectional profile of a tunnel two factors 
have to be taken into consideration: (1) The form of section 
best suited to the conditions, and (2) the interior dimensions of 
this section. 



18 TUNNELING 

Form of Section. — The form of the sectional profile of a tun- 
nel should be such that the lining is of the best form to resist 
the pressures exerted by the unsupported walls of the tunnel 
excavation, and these vary with the character of the material 
penetrated. These pressures are both vertical and lateral in 
direction; the roof, deprived of support by the excavation, tends 
to fall, and the opposite sides for the same reason tend to slide 
inward along a plane more or less inclined, depending upon the 
friction and cohesion of the material. In some rocks the co- 
hesion is so great that they will stand vertically, while it may 
be very small in loose earth which slides along a plane whose 
inclination is directly proportional to the cohesion. 

From the theory of resistance of profiles we know that the 
resistance of a line to exterior normal forces is directly propor- 
tional to its degree of curvature, and consequently inversely 
proportional to the radius of the curve. Hence the sectional 
profile of a tunnel excavated through hard rock, where there 
are no lateral pressures owing to the great cohesion of the ma- 
terial, and having to resist only the vertical pressure, should 
be designed to ofTer the greatest resistance at its highest point, 
and the curve must, therefore, be sharper there, and may de- 
crease toward the base. In quicksand, mud, or other material 
practically without cohesion, the pressures will all be normal 
to the line of the profile, and a circular section is the one best 
suited to resist them. These theoretical considerations have 
been proved correct by actual experience, and they may be 
employed to determine in a general way the form of section to 
be adopted. Applying them to very hard rock, they give us 
a section with an arched roof and vertical side walls. In softer 
materials they give us an elliptical section with its major axis 
vertical, and in very soft quicksands and mud they give us the 
circular section. These three forms of cross-section and their 
modifications are the ones commonly employed for tunnels. 
An important exception to this general practice, however, is 
met with in some of the city underground rapid-transit rail- 



DETERMINING THE CENTER LINE 



19 



ways built of late years, where a rectangular or box section is 
employed. These tunnels are usually of small depth, so that 
the vertical pressures are comparatively light, and the bending 
strains, which they exert upon the flat roof, are provided for by 
employing steel girders to form the roof lining. 

From what has been said it will be seen that it is impossible 
to establish a standard sectional profile to suit all conditions. 
The best one for the majority of conditions, and the one most 
commonly employed, is a polycentric figure in which the num- 
ber of centers and the length of the radii are fixed by the engineer 
to meet the particular conditions which exist. In a general way 
this form of center may be considered as composed of two parts 
symmetrical in respect to the vertical axis. Fig. 7 shows such 
a profile, in which DH 
is the vertical axis. The 
section is unsymmetri- 
cal in respect to the 
horizontal axis GE. The 
upper part forming the 
roof arch is usually a 
semi-circle or semi-oval, 
while the lower part, 
comprising the side walls 
and invert of floor, varies 
greatly in outline. Sometimes the side walls are vertical and 
the invert is omitted, as shown by Fig. 8; and sometimes the 
side walls are inclined, with their bottoms braced apart by the 
invert, as shown by Fig. 9. In more treacherous soils the side 
walls are curved, and are connected by small curved sections 
to the invert, as shown by Fig. 10. In the last example the 
side walls are commonly called skewbacks, and the lower part 
of the section is a polycentric figure like the upper part, but 
dissimilar in form. 

In a tunnel section whose profile is composed entirely of 
arcs the following conditions are essential: The centers of the 




r>:-rr=4=.-t 



Fig. 7. — Diagram of Polycentric Sectional Profile. 



20 TUNNELING 

springer arcs Ga and Ea', Fig. 7, must be located on the line 
GE; the center of the roof arc hDh^ must be located on the axis 
HD) the total number of centers must be an odd number; the 



Fig. 8 Fig. 9 Fig. 10 

Figs. 8 to 10. — Typical Sectional Profiles for Tunnel. 

radii of the succeeding arcs from G toward D and E toward 
D must decrease in length, and finally the sum of the angles 
subtended by the several arcs must equal 180°. 

Dimensions of Section. — The dimensions to be given to the 
cross-section of a tunnel depend upon the purpose for which it 
is to be used. Whatever the purpose of the tunnel, the follow- 
ing three points have to be considered in determining the size 
of its cross-section: (1) The size of clear opening required; (2) 
the thickness of lining masonry necessary; and (3) the decrease 
in the clear opening from the deformation of the lining. 

Railway tunnels may be built either to accommodate one or 
two, three and four tracks. In single-track tunnels a clear space 
of at least 2 J ft. on each side should be allowed for between the 
tunnel wall and the side of the largest standard locomotive or 
car, and a clear space of at least 3 ft. should be allowed for be- 
tween the roof and the top of the same locomotive or car. Since 
the roof of the tunnel is arch-shaped, to secure a clearance of 3 ft. 
at every point will necessitate making the clearance at the center 
greater than this amount. In double-track tunnels the same 
amounts of side and roof clearances have to be provided for, 
and, in addition, there has to be a clearance of at least 2 ft. 
between trains. On the three- and four-track tunnels only the 
width varies while the height remains almost equal to the 
two track. Referring to Fig. 7, and assuming the line AB 



DETERMINING THE CENTER LINE 



21 



to represent the level of the tracks, then the ordinary dimensions 
in feet required for both single- and double-track tunnels are 
as follows : — 





Height, D. F. 

Feet. 


Width, G. E. 

Feet. 


Height, C. F. 

Feet. 


Height, C. H. 
Feet. 


Single track .... 
Double track . . . 


17.6 to 18 
26.6 to 28 


16.5 to 18 

26.6 to 28 


6 to 7.4 
6.3to6.9 


Ito iAB 
i to 1 A5 



The dimensions of tunnels built for aqueduct purposes are 
determined so as to have an area of cross-section equal to the 
required waterway. In the Croton Aqueduct two different types 
of cross-sections were used, the circular one for tunnels through 
rock and the horseshoe section for tunnels through loose ma- 
terials. In the Catskill aqueduct three different cross-sections 
have been selected, the circular one for tunnels under pressure 
and the horseshoe for tunnels at the hydraulic gradient. These, 
however, through rock have a cross-section formed of a semi- 
circular arch and vertical side walls, while through earth the semi- 
circular arch is supported by skewback walls. 

In tunnels built for railroad aqueduct sewer and any other 
purpose the thickness of the masonry lining to be allowed for 
varies with the material penetrated, as will be explained in a 
succeeding chapter where the dimensions for various ordinary 
conditions are given in tabular form. The lining masonry is 
subject to deformation in three ways : by the sinking of the whole 
masonry structure, by the squeezing together of the side walls 
by the lateral pressures, and by the settling of the roof-arch. 
The whole masonry structure never sinks more than three or 
four inches, and merits little attention. The movement of the 
side walls towards each other, which may amount to three or 
four inches for each wall without endangering their stability, 
has, however, to be allowed for; and similar allowance must be 
made for the settling of the roof-arch, which may amount to 
from nine inches to two feet, when the arch is built first as in 
the Belgian system and rests for some time upon the loose soil. 



22 



TUNNELING 



CHAPTER III. 

EXCAVATING MACHINES AND ROCK DRILLS 
EXPLOSIVES AND BLASTING. 



Earth-Excavating Machines. — Comparatively few of the labor- 
saving machines employed for breaking up and removing loose 
soil in ordinary surface excavation are used in tunnel excava- 
tion through the same material. Several forms of tunnel 
excavating machines have been tried at various times, but only 
a few of them have attained any measure of success, and these 
have seldom been employed in more than a single work. In 
the Central London underground railway work through clay a 
continuous bucket excavator (Fig. 11) was employed with 




Fig. 11.— Soft Ground Bucket Excavating Macliine : Central London Underground Railway. 

considerable saving in time and labor over hand work. In 
some recent tunnel work in America the contractors made 
quite successful use of a modified form of steam shovel. These 
are the most recent attempts to use excavating machines in 
soft ground, and they, like all previous attempts, must be 
classed as experiments rather than as examples of common 
practice. The Thomson machine,* however, can be employed 

* The machine was designed by Mr. Thomas Thomson, Engineer for Messrs. Walter 
Scott & Co. 



EXCAVATING MACHINES AND ROCK DRILLS 23 

in any tunnel driven through loose soil. It occupies a compara- 
tively small space and may easily work when the timbering is 
used to support the roof of the tunnel. Steam shovel instead 
may give efficient result only in the case that the whole section 
of the tunnel is open at once and there are no timbers to prevent 
the free swinging of the dipper handle and boom. But in tunnels 
through loose soils it is almost impossible to open the whole 
section at once without the necessity of supporting the roof. 
Consequently the use of steam shovel in loose tunnels is very 
limited. The shovel, the spade, and the pick, wielded by hand, 
are the standard tools now, as in the past, for excavating soft- 
ground tunnels. 

Rock-Excavating Machines. — At one period during the work 
of constructing the Hoosac tunnel considerable attention was 
devoted to the development of a rock excavating, boring, or 
tunneling machine. This device was designed to cut a groove 
around the circumference of the tunnel thirteen inches wide 
and twenty-four feet in diameter by means of revolving cutters. 
It proved a failure, as did one of smaller size, eight feet in 
diameter, tried subsequently. During and before the Hoosac 
tunnel work a number of boring-machines of similar character 
were experimented with at the Mont Cenis tunnel and elsewhere 
in Europe; but, like the American devices, they were finally 
abandoned as impracticable. 

Hand Drills. — Briefly described, a drill is a bar of steel 
having a chisel-shaped end or cutting-edge. The simplest form 
of hand drill is worked by one man, who holds the drill in one 
hand, and drives it with a hammer wielded by his other hand. 
A more efficient method of hand-drill work is, however, where 
one man holds the drill, and another swings the hammer or 
sledge. Another form of hand drill, called a churn drill, con- 
sists of a long, heavy bar of steel, which is alternately raised 
and dropped by the workman, thus cutting a hole by repeated 
impacts. 

In drilling by hand the workman holding the drill gives it a 



24 TUNNELING 

partial turn on its axis at every stroke in order to prevent wedg- 
ing and to offer a fresh surface to the cutting-edge. For 
the same reason the chips and dust which accumulate in the 
drill-hole are frequently removed. The instruments used for 
this purpose are called scrapers or dippers, and are usually 
very simple in construction. A common form is a strong wire 
having its end bent at right angles, and flattened so as to 
make a sort of scoop by which the drilHngs may be scraped 
or hoisted out of the hole. It is generally advantageous to 
pour water into the drill-hole while drilling to keep the drill 
from heating. 

Power Drills. — When the conditions are such that use can 
be made of them, it is nearly always preferable to use power 
drills, on account of their greater speed of penetration and 
greater economy of work. Power drills are worked by direct 
steam pressure, or by compressed air generated by steam or 
water power, and stored in receivers from which it is led to the 
drills through iron pipes. A great variety of forms of power 
drills are available for tunnel work in rock, but they can nearly 
all be grouped in one of two classes: (1) Percussion drills, and 
(2) Rotary drills. 

Percussion Drills. — The first American percussion drill 
was patented by Mr. J. J. Couch of Philadelphia, Penn., in 
March, 1849. In May of the same year, Mr. Joseph W. Fowle, 
who had assisted Mr. Couch in developing his drill, patented a 
percussion drill of his own invention. The Fowle drill was 
taken up and improved by Mr. Charles Burleigh, and was first 
used on the Hoosac tunnel. In Europe Mr. Cave patented 
a percussion drill in France in October, 1851. This invention 
was soon followed by several others; but it was not until Som- 
meiller's drill, patented in 1857 and perfected in 1861, was used 
on the Mont Cenis tunnel, that the problem of the percussion 
drill was practically solved abroad. Since this time numerous 
percussion drill patents have been taken out in both America 
and Europe. 



EXCAVATING MACHINES AND ROCK DRILLS 25 

A percussion drill consists of a cylinder, in which works a 
piston carrying a long piston rod, and which is supported in 
such a manner that the drill clamped to the end of the piston 
rod alternately strikes and is withdrawn from the rock as the 
piston reciprocates back and forth in the cylinder. Means are 
devised by which the piston rod and drill turn slightly on their 
axis after each stroke, and also by w^hich the drill is fed for- 
ward or advanced as the depth of the drill-hole increases. The 
drills of this type which are in most common use in America 
are the Ingersoll-Sergeant and the Rand. There are various 
other makes in common use, however, which differ from the 
two named and from each other chiefly in the methods by 
which the valve is operated. All of these drills work either 
with direct steam pressure or with compressed air. Workable 
percussion drills operated by electricity are built, but so far 
they do not seem to have been able to compete commercially 
with the older forms. No attempt will be made here to make 
a selection between the various forms of percussion drills for 
tunnel work, and for the differences in construction and the 
merits claimed for each the reader is referred to the makers of 
these machines. All of the leading makes will give efficient 
service. It goes almost without saying that a good percussion 
drill should operate with little waste of pressure, and should 
be composed of but few parts, which can be easily removed and 
changed. 

Drill Mountings. — For tunnel work the general European 
practice is to mount power drills upon a carriage moving on 
tracks in order that they be easily withdrawn during the firing 
of blasts. Connection is made with the steam or compressed 
air pipes by means of flexible hose which can easily be attached 
or detached as the drill advances or when it is moved for repairs 
or during blasts. Two, four, and sometimes more drills are 
mounted and work simultaneously on a single carriage. In 
America it has been found that column mountings have been 
more successful for tunnel work than any other form. The 



26 



TUNNELING 



column mounting made by the Ingersoll-Sergeant Drill Co. 
is shown in Fig. 12. In using this form of mounting no tracks 
or other special apparatus is required; it is not necessary, as 




Fig. 12. — Column Mounting for Percussion Drill: Ingersoll-Sergeant Drill Go. 



is the case with the carriage mounting, to remove the debris 
before resuming operations, but as soon as the blasting has been 
finished and the smoke has sufficiently disappeared the column 
can be set up and drilling resumed. 



EXCAVATING MACHINES AND ROCK DRILLS 27 

Rotary Drills. — Rotary drilling machines, or more simply- 
rotary drills, were first used in 1857 in the Mont Cenis tunnel. 
The advantages claimed for rotary drills in comparison with 
percussion drills are: (1) That less power is required to drive 
the drill, and the power is better utihzed ; (2) once the machines 
work easily they do not require continual repairs, and (3) in 
driving holes of large size the interior nucleus is taken away 
intact, thus reducing work and increasing the speed of drilling. 
Rotary drills are extensively used for geological, mining, well- 
driving, and prospecting purposes; but they are very seldom 
employed in tunnels in America, although successfully used for 
this purpose in Europe. The reason they have not gained 
more favor among American tunnel builders is due to some 
extent perhaps to prejudice, but chiefly to the great cost of the 
machine as compared with percussion drills, and to the expense 
of diamonds for repairs. Those who advocate these machines 
for tunnel work point out, however, that under ordinary usage 
the diamonds have a very long hfe, — borings of 700 lin. ft. 
being recorded without repairs to the diamonds. 

The form of rotary drill used chiefly for prospecting pur- 
poses is the diamond drill. This machine consists of a hollow 
cyHndrical bit having a cutting-edge of diamonds, which is 
revolved at the rate of from two hundred to four hundred rev- 
olutions per minute by suitable machinery operated by steam 
or compressed air. The diamonds are 
set in the cutting-edge of the bit so as 
to project outward from its annular 
face and also slightly inside and outside 
of its cylindrical sides (Fig. 13). When 
the drill rod with the bit attached is 
rotated and fed forward the bit cuts an fig. is. -sketch of Diamond 

Drill Bit. 

annular hole into the rock ; the drillings 

being removed from the hole by a constant stream of water 
which is forced dowm through the hollow drill rod and emerges, 
carrying the debris with it, up through the narrow space between 




28 TUNNELING 

the outside of the bit and the walls of the hole. There are 
various makes of diamond drills, but they all operate in essentially 
the same manner. 

The rotary drill principally employed in Europe in tunneHng 
is the Brandt. The cutting-edge of the Brandt drill consists of 
hardened steel teeth. The bit is pressed against the rock by 
hydraulic pressure, and usually makes from seven to eight revo- 
lutions per minute. Some of the water when freed goes through 
the hollow bit, keeping it cool, and cleaning the hole of debris. 
A w^ater pressure of from 300 to 450 lbs. per square inch is 
required to operate these drills. Rotary rock-drills may be 
mounted either on carriages or on columns for tunnel work. 
Several machines have recently been constructed for the pur- 
pose of breaking the rock in tunnels without blasting, but they 
did not .meet the approval of tunnel engineers. One of these 
machines is provided with numerous electric torches, which are 
applied to the rock at the front. By suddenly chilling the rock 
with a stream of cold water the stone will crumble away. An- 
other machine was tested, with little success, in the excavation 
for the New Grand Central Depot in New York. On the face 
of this machine there is a multitude of chipping drills revolving 
on four arms and driven by air pressure. They attack the 
rock and chip it into fragments, which are carried away by an 
endless band. 

EXPLOSIVES AND BLASTING. 

When the holes are once drilled, either by hand or power 
drills, they are charged with explosives. The principal explo- 
sives employed in tunneHng are gunpowder, nitroglycerine, and 
dynamite. 

Gunpowder. — Gunpowder is composed of charcoal, sulphur, 
and saltpeter in proportions varying according to the quality of 
the powder. For mining purposes the composition employed 
is 65 % saltpeter, 15 % sulphur, and 20 % charcoal. It is a black 
granulated powder having a specific gravity of 1.5; the black 



EXCAVATING MACHINES AND ROCK DRILLS 29 

color is given by the charcoal; and the grains have an angular 
form, and vary in size from | in. to | in. Good blasting powder 
should contain no fine grains, which may be detected by pour- 
ing some of the powder upon a sheet of white paper. The 
force developed by the explosion of gunpowder is not accurately 
known; it depends upon the space in which it is confined. Dif- 
ferent authorities estimate the pressure at from 15,000 lbs. 
per sq. in. in loose blasts to 200,000 lbs. per sq. in. in gunnery. 
Authorities also differ in opinion as to the character of the gases 
developed by the explosion of gunpowder, a matter of vital 
concern to the tunnel engineer, since they are likely to affect 
the health and comfort of his workmen. It may be assumed 
in a general way, however, that the oxygen of the saltpeter 
converts nearly all of the carbon of the charcoal into carbon 
dioxide, a portion of which combines with the potash of the 
saltpeter to form carbonate of potash, the remainder con- 
tinuing in the form of gas. The sulphur is converted into 
sulphuric acid, and forms a sulphate of potash, which by reaction 
is decomposed into hyposulphite and sulphide. The nitrogen 
of the saltpeter is almost entirely evolved in a free state; and 
the carbon not having been wholly burnt into carbonic acid, 
there is a proportion of carbonic oxide. 

Nitroglycerine. — Nitroglycerine is one of the modern explo- 
sives used as a substitute for gunpowder. It is a fluid pro- 
duced by mixing glycerine with nitric and sulphuric acids; it 
freezes at +41° F., and burns very quietly, developing carbonic 
acid, nitrogen, oxygen, and water. By percussion or by the 
explosion of some substances, such as capsules of gunpowder 
or fulminate of mercury, nitroglycerine produces a sudden 
explosion in which about 1250 volumes of gases are produced. 
The pressure of these gases has been calculated at 26,000 at- 
mospheres, or 324,000 lbs. per sq. in. Nitroglycerine explodes 
very easily by percussion in its normal state, but with great 
difficulty when frozen; hence, in America, at the beginning 
of its use, it was transported only in a frozen state. When 



30 TUNNELING 

dirty, nitroglycerine undergoes a spontaneous decomposition 
accompanied by the development of gases and the evolution 
of heat, which, reaching 388° F., causes it to explode. Notwith- 
standing the enormous pressures which nitroglycerine develops, 
it is very seldom used in its liquid state, but is mixed with 
a granular absorbent earth composed of the shells of diatoms. 
The fluid undergoes no chemical change by being absorbed, 
and explodes, freezes, and burns under the same conditions as 
in the fluid state. 

Dynamite. — The credit of rendering nitroglycerine available 
for the purposes of the engineer by mixing it with a granular 
absorbent is due to Albert Nobel of Stockholm, Sweden, who 
named the new material dynamite. The nitroglycerine in 
dynamite loses very little of its original explosive power, but 
is very, much less easily exploded by percussion, and can be 
employed in horizontal as well as vertical holes, which was, of 
course, not possible in its Hquid state. Dynamite must contain 
at least 50 % of nitroglycerine. Some manufacturers, instead of 
using diatomaceous earth, use other absorbents which develop 
gases upon explosion and increase the force of the explosion. 
These mixtures are classed under the general name of false dyna- 
mites. A great many varieties of dynamite are manufactured, 
and each manufacturer usually makes a number of grades to 
which he gives special names. Dynamite for railway work, 
tunnehng, and mining contains about 50 % of nitroglycerine ; for 
quarrying about 35 %, and for blasting soft rocks about 30 %. 
It is sold in cylindrical cartridges covered with paper. 

Storage of Explosives, — In driving tunnels through rock 
large quantities of explosives must be used, and it is necessary 
to have some safe place for storing them. In many States 
there are special laws governing the transportation and storage 
of explosives; where there is no regulation by law the engineer 
should take suitable precautions of his own devising. It is 
best to build a special house or hut in one of the most con- 
cealed portions of the work and away from the tunnel, and 



EXCAVATING MACHINES AND ROCK DRILLS 31 

protect it with a lightning-rod and from fire. Strict orders 
should be given to the watchman in charge not to allow persons 
inside with lamps or fire in any form, and smoking should be 
prohibited. The use of hammers for opening the boxes should 
be prohibited; and dynamite, gunpowder, and fulminate of 
mercury should not be stored together in the same room. A 
quantity of dynamite for two or three days' consumption may 
be stored near the entrance of the tunnel in a locked box, the 
keys of which are kept by the foreman of the work. When 
dynamite has been frozen the engineer should provide some 
arrangement by which it may be heated to a temperature not 
exceeding 120° F., and absolutely forbid it being thawed out on 
a stove or by an open fire. 

Fuses. — When gunpowder is used in tunnehng it is ignited 
by the Blickford match. This match, or fuse as it is more 
commonly called, consists of a small rope of yarn or cotton 
having as a core a small continuous thread of fine gunpowder. 
To protect the outside of the fuse from moisture it is coated 
with tar or some other impervious substance. These fuses are so 
w^ell made that they burn very uniformly at the rate of about 
1 ft. in 20 seconds, hence the moment of explosion can be pretty 
accurately fixed beforehand. Blickford matches have the ob- 
jection for tunnel work of burning with a bad odor, especially 
when they are coated with tar, and to remedy this many others 
have been invented. Those of Rzika and Franzl are the best 
known of these. The former has many advantages, but it 
burns too quickly, about 3 ft. per second, and is expensive; 
the latter consists of a small hollow rope filled with dynamite. 

Bhckford matches cannot be used to explode dynamite, the 
use of a cartridge being required. These cartridges are small 
copper cylinders containing fulminate of mercury. They may 
be attached to the end of the Blickford match, which being 
ignited the spark travels along its length until it reaches the 
copper cylinder, where it explodes the fulminate of mercury, 
which in turn explodes the dynamite. Blasts may also be fired 



32 TUNNELING 

by electricity, which, in fact, is the most common and the 
preferable method, because several blasts can be fired simulta- 
neously, and because the current is turned on at a great dis- 
tance, thus affording greater safety to the workmen. 

The method of electric firing generally employed in America 
is known as the connecting series method, and consists in firing 
several mines simultaneously. The ends of the wdres are scraped 
bare, and the wire of the first hole of the series is twisted to- 
gether with the wire of the second hole, and so on; finally the 
two odd wires of the first and last holes are connected to two 
wires of a single cable or to two separate cables extending to 
some safe place to which the men can retreat. Here the two 
cable wires are connected by binding screws to the poles of a 
battery, or sometimes to a frictional electric machine. The cur- 
rent passes through the wires, making a spark at each break, and 
so fires the fulminate of mercury, which explodes the dynamite. 

Simultaneous firing by electricity by utilizing the united 
strength of the blasts at the same instant secures about 10 % 
greater efficiency from the explosives. Another advantage of 
electric firing is that in case of a missfire of any one of the 
holes there is slight possibility of explosion afterwards, and the 
place can be approached at once to discover the cause. 

Tamping. — Tamping is the material placed in the hole above 
the explosive to prevent the gases of explosion from escaping 
into the air. Tamping generally consists of clay. When gun- 
powder is used the clay must be well rammed with a wooden 
tool, and paper, cotton, or some other dry material must be 
placed betw^een the moist clay and the powder. When dyna- 
mite is used it is not necessary to ram the tamping, since the 
suddenness of the explosion shatters the rock before the clay 
can be driven from the hole. 

A few experienced men should be appointed to fire the blasts. 
These men should give ample warning previous to the blast in 
order that all machinery and tools which might be injured by fly- 
ing fragments may be removed out of danger, and so that the 



EXCAVATING MACHINES AND ROCK DRILLS 33 

workmen may seek safety. When all is ready they should 
fire the blasts, keeping accurate count of the explosions to 
ensure that no holes have missed fire, and should call the work- 
men back when all danger is over. In case any hole has missed 
fire it should be marked by a red lamp or flag. 

Nature of Explosions. — When the explosives are ignited a 
sudden development of gases results, producing a sudden and 
violent increase of pressure, usually accompanied by a loud 
report. The energy of the explosion is exerted in all directions 
in the form of a sphere having its center at the point of explo- 
sion, and the waves of energy lose their force as the distance 
from this central point increases. The energy of the explosion 
at any point in the sphere of energy is, therefore, inversely 
proportional to the distance of this point from the center of 
explosion. In the vicinity of the center of explosion the gases 
have sufficient power to destroy the force of cohesion and 
shatter the rock; further on, as they lose strength, they only 
destroy the elasticity of the material and produce cracks; and 
still further away they only produce a shock, and do not affect 
the material. Within the sphere of energy there are, therefore, 
three other concentric spheres: the first one being where 
cohesion is destroyed, the second where elasticity is overcome, 
and the third where the shock is transmitted by elasticity. 
When the latter sphere comes below the surface, the gases 
remain inside the rock; but when the surface intersects either 
of the other two spheres, the gases blow up the rock, forming a 
cone or crater, whose apex is at the point of explosion, and 
which is called the blasting-cone. The larger the blasting-cone 
is, the greater is the amount of rock broken up; and .the object 
of the engineer should, therefore, always be so to regulate the 
depth of the hole and the quantity of explosive as to secure the 
largest possible blasting cone in each case. Experiments are 
required to determine the most efficient depth of hole, and 
quantity of explosive to be employed, since these differ in 
different kinds of rock, with the position of the rock strata, 



34 TUNNELING 

etc.; but in ordinary practice, the depths of the holes are made 
from 2 to 3 ft. in the heading and upper portion of the tunnel, 
when drilled by hand; and from 6 to 8 ft. when drilled by power 
drills. In the lower portion of the profile, the holes are made 
deeper, from 3 ft. to 4 ft. when drilled by hand, and exceeding 6 
ft. when drilled by power. The distance of the holes apart should 
be about equal to the diameter of the blasting-cone ; as a general 
rule it is assumed that the base of the blasting-cone has a diam- 
eter equal to twice the depth of the hole. The following table 
gives the average number of holes required in each part of the 
excavation for the St. Gothard tunnel in which the heading 
was excavated by machine drills while the other parts were 
excavated by hand drills : 

NO. OF PAKT.* NAME OF PABT. NO. OF HOLES 

1. Heading 6 to 9 

2. Right wing of heading 3to5 

3. Left wing of heading 3 to 5 

4. Shallow trench with core 2 

5. Deepening of trench to floor 6 to 9 

6. Narrow mass of core to left 3 

7. Greater mass of core to left 6 to 9 

8. Culvert J 

Total section 30 to 43 

The quantity of explosives required for blasting depends 
upon the quality of the rock, since the force of the explosives 
must overcome the cohesion of the rock, which varies with its 
nature, and often differs greatly in rocks of the same kind and 
composition. The quantity of explosives required to secure 
the greatest efficiency in blasting any particular rock may be 
determined experimentally, but in practice it is usually deduced 
by the following rules: (1) The blasting force is directly pro- 
portional to the weight of the explosives used, and (2) the bulk 
of the blasted rock is proportional to the cube of the depth of 
the holes. It is usually assumed, also, that the explosive should 
fill at least one-fourth the depth of the hole. 

* The location of the parts numbered is shown by Fig. 14, p. 36. 



EXCAVATING MACHINES AND ROCK DRILLS 



35 



The following table gives the depth of holes and amount of 
dynamite used at each advance in the Fort George Tunnel 
illustrated on page 155. 



Order of Firing. 


Kinds of Holes. 


Depth. 


Charge. 


Kind of Dynamite. 


|-| 1 1st round 
«B |2nd round 

!>„ f3d round 
^^J4th round 
®K 1 5th round 


4 grading 

5 bench 

6 trimming 

8 center cut 
8 side 
6 dry 


3' to 5' 
9' 6" 
3' to 9' 

9' 

8' 
8' 


50 lbs. 
45 " 
42 " 

56 " 
48 " 
36 " 


40% climax 
40% - 
40% - 

60% " 
40% '' 
40% - 



36 



TUNNELING 



CHAPTER IV. 

GENERAL METHODS OF EXCAVATION: SHAFTS 
CLASSIFICATION OF TUNNELS. 



A NUMBEK of different modes of procedure are followed in 
excavating tunnels, and each of the more important of these 
will be considered in a separate chapter. There are, however, 
certain characteristics common to all of these methods, and 
these will be noted briefly here. 

Division of Section. — It may be asserted at the outset that 
the whole area of the tunnel section is not ordinarily excavated 
at one time, but that it is removed in sections, and as each 

section is excavated it is thoroughly 
timbered or strutted. The order in 
which these different sections are 
excavated varies with the method of 
excavation, and it is clearly shown 
for each method in succeeding chap- 
ters. As a single example to illus- 
trate the proposition just made, the 
division of the section and the se- 
quence of excavation adopted at the 
St. Gothard tunnel is selected (Fig. 
14). The different parts of the 
section were excavated in the order numbered ; the names given 
to each part, and the number of holes employed in breaking it 
down, are given by the table on page 34. Whatever method is 
employed, the work always begins by driving a heading, which 
is the most difficult and expensive part of the excavation. All 
the other operations required in breaking down the remainder 




Fig. 14. — Diagram Showing Sequence 
of Excavation for St. Gothard 
Tunnel. 



GENERAL METHODS OF EXCAVATION 37 

of the tunnel section are usually designated by the general 
term of enlargement of the profile. The various operations of 
excavation may, therefore, be classified either as excavation 
of the heading or enlargement of the profile. 

Excavation of the Heading. — There is considerable confusion 
among the different authorities regarding the exact definition 
of the term "heading" as it is used in tunnel work. Some 
authorities call a small passage driven at the top of the profile 
a heading, and a similar passage driven at the bottom of the 
profile a drift ; others call any passage driven parallel to the 
tunnel axis, whether at the top or at the bottom of the profile, 
a drift; and still others give the name "heading" to all such 
passages. For the sake of distinctness of terminology it seems 
preferable to call the passage a heading when it is located at 
the top of the profile, and a drift when it is located near the 
bottom. 

Headings and drifts are driven in advance of the general 
excavation for the following purposes : (1) To fix correctly 
the axis of the tunnel; (2) to allow the work to go on at 
different points without the gangs of laborers interfering with 
each other ; (3) to detect the nature of material to be dealt with 
and to be ready in any contingency to overcome any trouble 
eaused by a change in the soil ; and (4) to collect the water. 
The dimensions of headings in actual practice vary according 
to the nature of the soil through which they are driven. As 
a general rule they should not be less than 7 ft. in height, so as 
to allow the men to work standing, and have room left for the 
roof strutting. The width should not be less than 6 ft., to 
allow two men to work at the front, and to give room for 
the material cars without interfering with the wall strutting. 
Usually headings are made 8 ft. wide. The length of headings 
in practice varies according to circumstances. In very long 
tunnels through hard rock the headings are sometimes ex- 
cavated from 1000 ft. to 2000 ft. in advance, in order that they 
may meet as soon as possible and the ranging of the center line 



38 



TUNNELING 



be verified, and so that as great an area of rock as possible may 
be attacked at the same time in the work of enlarging the 
profile. In short tunnels, where the ranging of the center line 
is less liable to error, shorter headings are employed, and in soft 
soils they are made shorter and shorter as the cohesion of the soil 
decreases. When the material has too little cohesion to stand 
alone, the tops and sides of the heading require to be supported 
by strutting. To prevent caving at the front of the heading, 
the face of the excavation is made inclined, the inclination 
following as near as may be the natural slope of the material. 

Enlargement of the Profile. — The enlargement of the profile 
is accomplished by excavating in succession several small 

prisms parallel to the heading, and 
its full length, which are so located 
that as each one is taken out the 
cross-section of the original heading 
is enlarged. The number, location, 
and sequence of these prisms vary 
in different methods of excavation, 
and are explained in succeeding 
chapters where these methods are 
described. To direct the excava- 
tion so as to keep it always within 
the boundaries of the adopted pro- 
file, the engineer first marks the center line on the roof of the 
heading by wooden or metal pegs, or by some other suitable 
means by which a plumb line may be suspended. He next 
draws to a large scale a profile of the proposed section; and 
beginning at the top of the vertical axis he draws horizontal 
lines at regular intervals, as shown by Fig. 15, until they inter- 
sect the boundary lines of the profile, and designates on each 
of these lines the distance between the vertical axis and the 
point where it intersects the profile. It is evident that' if the 
foreman of excavation divides his plumb line in a manner corre- 
sponding to the engineer's drawing, and then measures horizon- 




Fig. 15 — Diagram Showing Manner 
of Determining Correspondence of 
Excavation to Sectional Profile. 



GENERAL METHODS OF EXCAVATION 



39 



tally and at right angles to the vertical center plane of the 
tunnel the distance designated on the horizontal lines of the 
drawing, he will have located points on the profile of the sec- 
tion, or in other words have established the limits of excava- 
tion. 

In the excavation of the Croton Aqueduct for the water 
supply of New York city, an instrument called a polar pro- 
tractor was used for determining the location of the sectional 




Fig. 16.— Polar Protractor for Determining Profile of Excavated Cross-Section. 

profile. It was invented by Mr. Alfred Craven, division engi- 
neer of the work. This instrument consists of a circular disk 
graduated to degrees, and mounted on a tripod in such a manner 
that it may be leveled up, and also have a vertical motion and a 
motion about the vertical axis. The construction is shown 
clearly by Fig. 16. In use the device is mounted with its 
center at the axis of the tunnel. A light wooden measuring- 
rod tapering to a point, shod with brass and graduated to feet 
and hundredths of a foot, lies upon the wooden arm or rest, 
which revolves upon the face of the disk, and slides out to 



40 TUNNELING 

a contact with the surface of the excavation at such points 
as are to be determined. If the only information desired is 
whether or not the excavation is sufficient or beyond the es- 
tablished lines, the rod is set to the proper radius, and if it 
swings clear the fact is determined. If a true copy of the 
actual cross-section is desired, the rod is brought into contact 
with the significant points in the cross-section, and the angles 
and distances are recorded. 

The general method of directing the excavation in enlarging 
the profile by referring all points of the profile to the vertical 
axis is the one usually employed in tunneling, and gives good 
results. It is considered better in actual practice to have the 
excavation exceed the profile somewhat than to have it fall 
short of it, since the voids can be more easily filled in with 
riprap than the encroaching rock can be excavated during the 
building of the masonry. In tunnels where strutting is neces- 
sary the excavation must be made enough larger than the 
finished section to provide the space for it. In soft-ground 
tunnel's it is also usual to enlarge the excavation to allow for 
the probable slight sinking of the masonr}^ The proper allow- 
ance for strutting is usually left to the judgment of the fore- 
man of excavation, but the allowance for settlement must be 
fixed by the engineer. 

SHAFTS. 

Shafts are vertical walls or passages sunk along the line of 
the tunnel at one or more points between the entrances, to 
permit the tunnel excavation to be attacked at several different 
points at once, thus greatly reducing the time required for 
excavation. Shafts may be located directly over the center 
of the tunnel or to one side of it, and, while usually vertical, 
are sometimes inclined. During the construction of the tunnel 
the shafts serve the same purpose as the entrances ; hence they 
must afford a passageway for the excavated materials, which 



GENERAL METHODS OF EXCAVATION 41 

have to be hoisted out, and also for the construction tools and 
materials which have to be lowered down them. They must 
also afford a passageway for workmen, draft animals, and for 
pipes for ventilation, water, compressed air, etc. The character 
of this traffic indicates the dimensions required, but these de- 
pend also upon the method of hoisting employed. Thus, when 
a vdndlass or horse gin is used, and the materials are hoisted 
in buckets of small dimensions, the dimensions of the shaft may 
also be small; but when steam elevators are employed, and the 
material is carried on cars run on to the platform of the elevator, 
large dimensions must be given to the shaft. Generally the 
parts of the shaft used for different purposes are separated by 
partitions. The elevator for workmen and the various pipes 
are placed in one compartment, while the elevator for hoisting 
the excavated material and lowering construction material is 
placed in another. 

Shafts may be either temporary or permanent. They are 
temporary when they are filled in after the tunnel is completed, 
and permanent when they are left open to supply ventilation 
to the tunnel. Permanent shafts are usually made circular, and 
lined with brick, unless excavated in very hard and durable 
rock. When sunk for temporary use only, shafts are usually 
made rectangular with the greater dimension transverse to the 
tunnel. They are strutted with timber. A pump is generally 
located at the bottom of the shaft to collect the water which 
seeps in from the sides of the shaft and from the tunnel 
excavation. The dimensions of this pump will of course vary 
with the amount of water encountered, as will also the capacity 
of the pump for forcing it up and out of the shaft, which has 
always to be kept dry. 

The majority of engineers prefer to sink shafts directly 
over the center line of the tunnel. Side shafts are employed 
chiefly by French engineers. The chief advantage of the 
former method is the great facility which it affords for hoisting 
out the materials, while in favor of the latter method is the 



42 



TUNNELING 



non-interference of the shaft with the operations inside the 
tunnel. Were it not that the side shaft requires the intro- 
duction of a transverse gallery connecting it with the tunnel, 
it would be on the whole superior to the center shaft ; but the 
side gallery necessitates turning the cars at right angles, and 
consequently the use of a very sharp curve or a turntable to 
reach the shaft bottom, which is a disadvantage that may 
outweigh its advantages in some other respects. It is impos- 
sible to state absolutely which of these methods of locating 
shafts is the best ; both present advantages and disadvantages, 
and the use of one or the other is usually determined more by 
the local conditions than by any general superiority of either. 

When side shafts are employed they are sometimes made 
inclined instead of vertical. This form is used when the depth 
of the shaft is small. By it the hauling is greatly simplified, 
since the cars loaded at the front with excavated material can 
be hauled directly out of the shaft and to the dumping-place, 
surmounting the inclined shaft by means of continuous cables. 
The short galleries connecting the side shafts with the tunnel 
proper usually have a smaller section than the tunnel, but are 
excavated in exactly the same manner. Another form of side 
shaft sometimes used is one reaching to the surface when 
the tunnel runs close to the side of cliff, as is the case with 
some of the Alpine railway tunnels. 

CLASSIFICATION OF TUNNELS. 

Tunnels are classified in various ways, but the most logical 
method would appear to be a grouping according to the quality 
of the material through which they are driven ; and this method 
will be adopted here. By this method we" have first the fol- 
lowing general classification : (1) Tunnels in hard rock ; (2) 
tunnels in ordinary loose soil; (3) tunnels in quicksand; 
(4) open-cut tunnels ; and (5) submarine tunnels. It is hardly 
necessary to say that this classification, like all others, is simply 



GENERAL METHODS OF EXCAVATION 43 

an arbitrary arrangement adopted for the sake of order and 
convenience in treating the subject. 

Tunnels in Hard Rock. — With the numerous labor-saving 
methods and machines now available, hard rock is perhaps the 
safest and easiest of all materials through which to drive a 
tunnel. Tunnels through hard rock may be excavated, either 
by a drift or by a heading. The difference depends upon 
whether the advance gallery is located close to the floor or 
near the soffit of the section. 

Tunnels in Loose Soils. — In driving tunnels through loose 
soils many different methods have been devised, which may be 
grouped as follows : (1) Tunnels excavated at the soffit — 
Belgian method; (2) tunnels excavated along the perimeter 

— German method; (3) tunnels excavated in the whole section 

— English, Austrian and American methods; (4) tunnels exca- 
vated in two halves independent of each other — Italian method. 

(1) Excavating the tunnel by beginning at the soffit of 
the section, or by the Belgian method, is the method ^of tunnel- 
ing in loose soils most commonly employed in Europe at the 
present time. It consists in excavating the soffit of the 
section first ; then building the arch, which is supported upon 
the unexcavated ground ; and finally in excavating the lower 
portion of the section, and building the side walls and 
invert. 

(2) In excavating tunnels along the perimeter an annular 
excavation is made, following closely the outhne of the sec- 
tional profile in which the lining masonry is built, after which 
the center core is excavated. In the German method two 
drifts are opened at each side of the tunnel near the bottom. 
Other drifts are excavated, one above the other, on each side 
to extend or heighten the first two until all the perimeter is 
open except across the bottom. The masonry lining is then 
built from the bottom upwards on each side to the crown of 
the arch, and then the center core is removed and the invert 
is built. 



44 TUNNELING 

(3) This method, as its name implies, consists in taking 
out short lengths of the whole sectional profile before begin- 
ning the building of the masonry. In the English method 
the invert is built first, then the side walls, and finally the 
arch. The excavators and masons work alternately. The 
Austrian method differs in two particulars from the EngHsh: 
the length of section opened is made great enough to allow the 
excavators to continue work ahead of the masons, and the side 
walls and roof are built before the invert. In the American 
method the whole section of the tunnel is open a,t once : exca- 
vators and masons work simultaneously, hut a very large 
quantity of timbering is required. / 

(4) The Italian method is very seldonz employed on account 
of its expensiveness, but it can often be used where the other 
methods fail. It consists in excavating the lower haK of the 
section, and building the invert and side walls, and then filling 
the space between the walls in again except for a narrow 
passageway for the cars ; next the upper part of the section is 
excavated, as in the Belgian method, and the arch is built ; and 
finally the soil in the lower part is permanently removed. 

Tunnels in Quicksand. — Tunnels through quicksand are 
driven by one of the ordinary soft-ground methods after drain- 
ing away the water, or else as submarine tunnels. 

Open-Cut Tunnels. — Open-cut tunnels are those driven at 
such a small depth under the surface that it is more convenient 
to excavate an open cut, build the tunnel masonry inside it, 
and then refill the open spaces, than it is to carry on the work 
entirely underground. In firm soils the usual mode of opera- 
tion is to excavate first two parallel trenches for the side walls, 
then remove the core, and build the arch and the invert. In 
unstable soils, since the invert must be built first, it is usual 
to open up a single wide trench. In infrequent cases where 
a tunnel is desired in a place which is to be filled in, the 
masonry is built as a surface structure, which in due time is 
covered. 



GENERAL METHODS OF EXCAVATION 



45 



Submarine Tunnels. — The mode of procedure followed in 
excavating submarine tunnels depends upon whether the mate- 
rial penetrated is pervious or impervious to water. In imper- 
vious material any of the ordinary methods of tunneling found 
suitable may be employed. In pervious material the excava- 
tion may be accomplished either by means of compressed air 
to keep the water out of the excavation, or by means of a 
shield closing the front of the excavation, or by a combination 
of these tw^o methods. Tunnels on the river bed are built by 
means of coffer dams which inclose alternate portions of the 
work, by sinking a continuous series of pneumatic caissons and 
opening communication between them, and by sinking the tunnel 
in sections constructed on land. 



In hard rock. 



In loose soil. < 



Methods of 

Excavating <! 
Tunnels. 



( By drifts. 
/ By a heading. 
By upper half: 

the arch is built be- 
fore the side walls. 
By the perimeter: 
excavated and lined 
before the central 
nucleus is removed. 

By whole section : 
the lining- begins after 
the whole section is 
excavated. 

By halves : 

the lower half is ex- 
cavated and lined, 
followed by the work 
of the upper half. 



Y Belgian method. 
J 

> German method. 

English method. 
Austrian method. 
1^ American method. 



> Italian method. 



In quicksand. 



Open-cut 
tunnels. 



Submarine 
tunnels. 



Ill resistant soils. 

In loose soils. 
^ Built up. 

' At great depths under 
the river bed. 

At small depths 
under the river bed. 



On the riverbed."^ 



By two lateral nar- 
row trenches. 

By one very large 
trench. 

By slices. 

By any method. 

f By shield. 
J By compressed air. 

I By shield and com- 

[ pressed air. 

f By coffer dams. 
J By pneumatic cais- 

j sons. 

t By built-up sections. 



46 TUNNELING 

The above diagram gives in compact form the classifica- 
tion of tunnels according to materials penetrated and methods 
of excavation adopted, which have been described more fully 
in the succeeding paragraphs. It may be noted here again that 
this is a purely arbitrary classification, and serves mostly as a 
convenience in discussing the different classes of tunnels with- 
out confusion. 



TIMBERING OR STRUTTING TUNNELS 47 



CHAPTER V. 

METHODS OF TIMBERING OR STRUTTING 
TUNNELS. 



The purpose of timbering or strutting in tunnel work is to 
prevent the caving-in of the roof and side walls of the exca- 
vation previous to the construction of the lining. As the 
strutting has to resist all the pressures developed in the roof 
and side walls, which may be exceedingly troublesome and 
of great intensity in loose soils, its design and erection call 
for particular care. The method of strutting adopted depends 
upon the method of excavation employed; but in every case 
the problem is not only to build it strong enough to withstand 
the pressures developed, but to do this as economically as 
possible, and with as little hindrance as may be to the work 
which is going on simultaneously and which will come later. 
Only the latter general problems of strutting peculiar to all 
methods of tunnel work will be considered here. For this 
consideration strutting may be classified according to the 
material of which it is built, under the heads of timber struc- 
tures and iron structures. 

TIMBER STRUTTING. 

Timber is nearly always employed for strutting in tunnel 
work. So long as it has the requisite strength, any kind of 
timber is suitable for strutting, since, it being only temporarily 
employed, its durability is a matter of slight importance. 
Timber with good elastic properties, like pine or spruce, is 
preferably chosen, since it yields gradually under stress, thus 



48 TUNNELING 

warning the engineer of the approach of danger ; while oak and 
other strong timbers resist until the last moment, and then 
yield suddenly under the breaking load. Soft woods, moreover^ 
are usually lighter in weight than hard woods, which is a con- 
siderable advantage where so much handling is required in 
a restricted space. Round timbers are generally employed, 
since they are less expensive, and quite as satisfactory in other 
respects as sawed timbers. In the English and Austrian 
methods of strutting, which are described further on, a few 
of the principal struts are of sawed timbers. 

The various timbers of the strutting are seldom 

attached by framed joints, but wedges are used 

to give them the necessary 

bearing against each other. 

Where framed joints are em- 

FiG.iT.-joining Tunnel struts ployed the v are made of the 

by Halving. f J J 

simplest form usually by 

11- -, . . . .1 1 ^ ^. ^^ FlG.18. -Round 

halving the joining timbers, as shown by Fig. 17. Timber post 
Fig. 18 shows a form of joint used where round ^^"^^capBear- 
posts carry beams of similar shape. The reason why 
it is possible to do away with jointed connections to such a 
great extent, is that the strains which the timbers have to 
resist are either compressive or bending strains, and because 
the timbers are so short that they do not require to be spliced. 
Strutting of Headings. — The method of strutting the head- 
ing that is employed depends upon the material through which 
the heading is driven. In solid rock strutting may not be 
required at all, or only for the purpose of preventing the 
fall of loose blocks from the roof, then vertical props are 
erected where required, or horizontal beams are inserted into 
the side walls, as shown by Fig. 19. These horizontal beams 
may be used singly at dangerous places, or they may be placed 
from 2 ft. to 3 ft. apart all along the heading. In the latter 
case they usually carry a lagging of planks, which may be 
placed at intervals or close together, and filled above with 



Tl^lBElilNG Oil STIIUTTING TUNNELS 



49 



stone in case the roof of the excavation is very unstable. 
Planks used in this manner are usually called poling-boards. 
Where the side walls as well as the roof require support, 





Fig, 19. — Ceiling Strutting for 
Tunnel Koofs, 



Fig. 20. 



Ceiling Strutting with Side 
Post Supports. 



vertical side posts are employed to carry the roof beams, as 
shown by Fig. 20; and, when necessary, poling-boards are 
inserted between these posts and the walls of the excavation. 

Frame Strutting. — In very loose soils not only the roof and 
side Avails, but also the floor of the heading require strutting. 





Fig. 21. — Sill, Side Post and Cap 
Cross Frame Strutting. 



Pig. 22. — Reinforced Cross Frame 
Strutting for Treacherous Materials. 



In these cases frame strutting is employed, as shown by Fig. 
21. It consists simply of a rectangular frame; at the top 
there is a crown bar supported by two vertical side posts 



50 



TUNNELLSG 



setting on a sill laid across the bottom of the heading. These 
frames are spaced at close intervals, and carry longitudinal 
planks or poling-boards. The sill of the frame is sometimes 
omitted when the soil is stable enough to permit it, and in its 
place Avooden footing blocks are substituted to carry the side 
posts. In soils where the pressures are great enough to bend 
the crown bar, a secondary frame is employed, as shown by 
Fig. 22, the two inclined roof members, or rafters, of which 
support the crown bar at the center. 

It is the more common practice in driving headings through 
soft soils to use inclined poling-boards to support the roof. 




m!^ 


^ 


m 


-^ 




^^^^^^=--^= 


^^ — 


W!^ 






r^ 


1 








M 






P 


1 






1 


'-'•^ 


f^0^^W^ym 





Fig. 23. — Longitudinal Poling-Board Sys- 
tem of Roof Strutting. 



Fig. 24. — Transverse Poling-Board System 
of Roof Strutting. 



Fig. 23 shows one method of doing this. The method of 
operation is as follows : Assuming the poling-boards a and b 
to be in place, and supported by the frames A, B (7, as shown, 
the first step in continuation of the work is to insert the 
poling-board c over the crown bar of frame (7, and under the 
block m. Excavation is then begun at the top, and as fast as 
the soil is removed ahead of it the poling-board c is driven 
ahead until its rear end only slightly overhangs the crown bar 
of frame C. The remainder of the face of the heading is then 
excavated nearly to the front end of the poling-board c, and 
another frame is set up. By a succession of these operations 



TIMBERING OR STRUTTING TUNNELS 51 

the heading is advanced. The poling-boards at the sides of 
the heading are placed in a similar manner to the roof poling- 
boards. A second method of using inclined poling-boards is 
shown by Fig. 24. Here the poling-boards run transversely, 
and are supported by the arrangement of timbering shown. 
The chief advantage of using these inclined poling-boards, 
particularly in the manner shown by Fig. 23, is that the 
excavators work under cover at all times, and are thus safe 
from falling fragments or sudden cavings. 

Box Strutting. — In very treacherous soils, such as quick- 
sand, peat, and laminated clay, box strutting is commonly em- 
ployed. The method of building this strutting is to set up at 
the face of the work a rectangular frame, and use it as a guide 
in driving a lagging or boxing of horizontal planks into the 
soft soil ahead. These planks have sharp edges, and are driven 
to a distance of 2 ft. or 3 ft. into the face of the heading, so as 
to inclose a rectangular body of earth. This earth is excavated 
nearly to the ends of the planks, and then another frame is 
inserted close up against the new face of the excavation, which 
supports the planks so that the remainder of the earth included 
by them may be removed. These two frames, with their plank 
lagging, constitute a " box ; " and a series of these boxes, one 
succeeding another, form the strutting of the heading. 

Strutting the Face. — In some cases it is found necessary 
to strut the face of the heading in order to prevent it from 
caving in. This is generally done by setting plank vertically, 
and bracing them up by means of inclined props whose feet 
abut against the sill of the nearest cross frame. This strutting 
is erected while the workmen are placing the side and roof 
strutting, and is removed to permit excavation. 

Full Section Timber Strutting. — For strutting the full section 
two forms of timbering are employed, known as the polygonal 
system and the longitudinal system. 

Longitudinal strutting consists of a timber structure so 
arranged as to have all the principal members supporting the 



52 



TUNNELING 



poling-boards parallel to the axis of the tunnel. This system 
of strutting is peculiar to the English method of tunneling. 
The longitudinal timbers rest on this finished masonry at one 
end, and are carried on a cross frame or by props at the other 
end. At intermediate points the longitudinals are braced 
apart by struts in planes transverse to the tunnel axis. This 
construction makes a very strong strutting framework, since 
the transverse struts act as arch ribs to stiffen the longitu- 
dinals ; but the use of transverse poling-boards requires the 
excavation of a larger cross-section than is necessary when longi- 
tudinal poling-boards are employed, and this increases the 
cost both for the amount of earth excavated and the greater 
quantity of filling required. 

In polygonal strutting the main members are in a plane 
normal to the axis of the tunnel. They form a polygon whose 
sides follow closely the sectional profile of the excavation. 
These polygonal frames are placed at more or less short inter- 
vals apart, and are braced together by short longitudinal struts 
lying close to the sides of the excavation, and running from 
one frame to the next, and also by longer longitudinal members 
which extend over several frames. The polygonal system of 
strutting is peculiar to the Austrian method of tunneling, and 
is fully described in a succeeding chapter. One of its distinc- 
tive characteristics is that 
the poling-boards are in- 
serted parallel to the tunnel 
axis. Polygonal strutting 
is generally held to be 
stronger than longitudinal 
strutting under uniform 
loads, but it is more liable 
to distortion when the 
loads are unsymmetrical. 
Strutting of Shafts. — Tunnel shafts are strutted both to 
prevent the caving-in of the sides and to divide them into 




Fig. 25,— Shaft with Single Transverse 
Strutting. 



TIMBEKING OR STRUTTING TUNNELS 



53 




compartments. When the material penetrated is very compact, 
and caving is not likely, a single series of transverse struts, one 
above the other, running from the top to the bottom of the 
shaft, as shown by Fig. 25, is used to divide it into two com- 
partments. In softer material, where the sides of the shaft 
require support, Fig. 26 
shows a form of strutting 
commonly employed. It 
consists of vertical corner 
posts braced apart at inter- 
vals by four horizontal struts 
placed close to the walls of 
the shaft. The long-er side 

^ Fig. 26.— Rectangular Frame Strutting for Shafts. 

struts are also braced apart 

at the center by a middle strut which divides the shaft into 
two compartments. A lagging of vertical plank is placed 
between the walls of the shaft and the horizontal side struts. 
In very loose soils the form of strutting shown by Fig. 27 is 
employed. This is practically the same construction as is 
shown by Fig. 26, with the addition of an interior polygonal 

horizontal bracing in each 
half of the shaft. Referring 
to Fig. 27, the timbers a^ «, 
etc., are vertical and con- 
tinuous from the top to the 
bottom of the shaft; and 
the horizontal timbers, 5, 5, 
etc., are spaced at more or 
less close intervals verti- 
cally. The lagging plank 
may be laid with spaces between them, or close together, or, 
in case of very loose material, with their edges overlapping. 
The manner of constructing the strutting is also governed by 
the stability of the soil. In firm soils it is possible to sink the 
shaft quite a depth vrithout timbering, and the timbering can 




Fig. 27. — Reinforced Rectangular Frame Strut- 
ting for Shafts in Treacherous Materials. 



54 



TUNNELING 



be erected in sections of considerable lengtb, which is always 
an advantage, but in loose soils the timbering has to follow 
closely the excavation. 

The solid wall shaft struttings which have been described 
are discontinued at the point where the shaft intersects the 
tunnel excavation ; and from this point to the floor of the 
tunnel an open timbering is employed, whose only duty is to 
support the weight of the solid strutting above. This timber- 
ing is made in various forms, but the most common is a timber 
truss or arch construction which spans the tunnel section. 

Quantity of Timber. — The quantity of timber employed in 
strutting a tunnel varies with the character of the material 
through which the tunnel is excavated : it is small for solid- 
rock tunnels, and large for soft-ground tunnels. In the Bel- 
gian method of excavation a smaller quantity of timber is 
used than in any of the other ordinary methods. For single- 
track tunnels excavated by this method there will be needed 
on an average about 3 to 3 J cu. yds. of timber per lineal foot 
of tunnel. Practical experience shows that about four-fifths of 
the timber once used can be employed for the second time. 
In any of the methods in which the whole tunnel section is 
excavated at once, the average amount of timber required per 
lineal foot is about 8.7 cu. yds. Of this amount about two- 
thirds can be used a second time. In the Italian method, in 
which the upper half and the lower half are excavated separately, 
about 5 cu. yds. of timber are required per lineal foot of tunnel, 
about one-half of which can be employed a second time. For 
qaicksand tunnels the amount of timbering required per lineal 
foot varies from 3 to 5 cubic yds. Shaft strutting requires 
from 1 to 1^ cu. yds. of timber per lineal foot. 

Dimensions of Timber. — The dimensions of the principal mem- 
bers composing the strutting of headings, full section, and 
shafts, are given in Table I. The planks used for lagging 
or the poling-boards are usually from 4 ins. to 6 ins. wide, 
with a length depending upon the method of strutting employed. 



TIMBERING OR STRUTTING TUNNELS 



55 



TABLE I. 

Showing Sizes of Various Timbers Used in Strutting Tunnels Driven 
Through Different Materials. 



Headings : 

Cap-pieces and vertical struts 

Sills 

Struts 

Distance apart of the frames in feet . . . 

Strutting of the tunnel, longitudinal strutting : 

Crown bars 

Props vertical or inclined supporting the crown 
bars 

Sills 

Cap-pieces or saddles 

Struts to stiffen the structure 

Distance apart of the frames (in feet) . . . 
Polygonal strutting : 

Cap-pieces and contour pieces 

Vertical struts on top 

Vertical struts below 

Intermediate sills 

Lower sills 

Raking props 

Distance apart of the frames (in feet) . . . 
Shafts : 

Horizontal beams forming the frame . . . . 

Transverse beams 

Vertical struts between the frames 

Struts to reenforce the frame 

Distance apart of the strutting (in feet) . . . 



Rock. 


Soft Soils. 


1 


1 


8 I 


6 

3 


>> «5 

S '8 


ins. 


ins. 


ins. 


ins. 


ins. 


6 


8 


10 


12 


14 






8 


10 


12 


5 


5 


6 


7 


8 


6 


4.5 


3 


2.6 


2.6 


12 


14 


14 






10 


12 


14 






8 


8 


10 






10 


12 


14 






6 


8 


10 






4.5 


4 


3 






8 


10 


12 


14 


16 


10 


12 


14 


16 


18 


12 


14 


16 


20 


24 


12 


14 


16 


20 


24 






12 


16 


18 


10 


10 


10 


12 


12 


6 


4.5 


4 


3 


3 


8 


8 


10 


12 


14 


8 


8 


8 


10 


12 


8 


8 


10 


12 


12 




6 


8 


8 


8 


6 


4.5 


4 


3 


2.6 



IRON STRUTTING. 

In 1862 Mr. Rziha employed old iron railway rails for 
strutting the IS'aensen tunnel, and his example was successfully 
followed in several tunnels built later where timber was scarce 



66 



TUNNELING 





Fig. 28. —Strut- 
ting of Timber 
Posts and Rail- 
way Rail Caps. 



Fig. 29. — Strutting 
made entirely of 
Railway Rails. 



and expensive. The advantages which iron strutting is claimed 
to possess over the more common wooden structure are : its 
greater strength ; the smaller amount of space which it takes 
up ; and the fact that it does not wear out, and may, therefore, 
be used over and over again. 

Iron Strutting in Headings. — In strutting the headings the 
cross frames have a crown bar consisting of a section of old 
railway rail carried either by wood or iron side posts. When 
wooden side posts are used their 
upper ends have a dovetail mor- 
tise, and are bound with an iron 
band, as shown by Fig. 28. The 
base of the rail crown bar is set 
into the dovetail mortise and 
fastened by wedges. When iron 
side posts are employed they 
usually consist of sections of rail- 
way rails, and the crown bar is 
attached to them by fish-plate connections, as 
shown by Fig. 29. The iron cross frames are set up as the 
heading advances, and carry the plank lagging or poling-boards, 
exactly in the same manner as the timber cross frames previ- 
ously described. 

Full Section Iron Strutting. — The iron strutting devised by 
Mr. Rziha for full section work is shown by Fig. 30. Briefly 
described, it consists of voussoir-shaped cast-iron segments, 
which are built up in arch form. Fig. 31 shows the construc- 
tion of one of the segments, all of which are alike, with the 
exception of the crown segment, which has a mortise and 
tenon joint which is kept open by filling the mortise with sand. 
The segments are bolted together by means of suitable bolt- 
holes in the vertical flanges, and when fully connected form an 
arch rib of cast iron. This arch rib, A, Fig. 30, carries a series 
of angle or T-iron frames bent into approximately voussoir 
shape, as shown at B, Fig. 30. Above these frames are inserted 



TIMBERING OR STRUTTING TUNNELS 



57 




Fig. 



). — Rziha's Combined Strutting and Centering 
of Cast Iron. 



the poling-boards, running longitudinally, and spanning the 
distance between consecutive arch ribs. By removing the bent 
iron frames the cast-iron rib forms a center upon which to con- 
struct the masonry. Fi- 
nally, to remove the cast- 
iron rib itself, the sand 
is drawn out of the mor- 
tise and tenon joint in 
the crown segment, which 
allows the joint to close, 
and loosen the segments 
so that they are easily 
unbutted. 

The illustration. Fig. 
30, shows longitudinal 
poling-boards ; more often 
longitudinal crown bars 

of railway rails span the space between connective arch ribs, 
and support transverse poUng-boards. In building the masonry, 
work is begun at the bottom on each side, the bent iron frames 
being removed one after another to give room for the masonry. 

As each frame is removed, it is 
replaced with a sort of screw- 
jack to support the poling-boards 
until the masonry is sufficiently 
completed to allow their removal. 
The interior bracing of the arch 
rib shown at a a and h h consists 
of railway rails carried by brack- 
ets cast on to the segments. A 
similar bracing of rails connects the successive arch ribs. These 
lines of bracing serve to carry the scaffolding upon which the 
masons work in building the lining. 

Iron Shaft Strutting. — In soft-ground shaft work, the use of 
an iron strutting, consisting of consecutive cast-iron rings, has 




Fig. 31. — Cast-iron Segment of Rziha's 
Strutting and Centering. 



58 



TUNNELING 



sometimes been employed to advantage. Fig. 32 shows the 
construction of one of these rings, which, it will be seen, is com- 
posed of four segments connected to each other by means of 
bolted flanges. The holes shown in the circumferential web of 
the ring are to allow for the seepage from the earth side walls. 

The method of placing this 
cylindrical strutting is to 
start with a ring having a 
cutting-edge. By means 
of excavation inside the 
ring, and by ramming, 
the ring is sunk into the 
ground a distance equal to 
its height. Another ring 
is then fastened by special hooks on top of the first one, and 
the sinking continued until the second ring is down flush with 
the surface. A third ring is then added, and so on until the 
entire shaft is excavated and strutted. As in timber shaft 
strutting, the solid iron ring strutting is carried down only to 
the top of the tunnel section, and below this point there is an 
open timber or iron supporting framework. 




Fig. 32. 



■Cast-iron Segmental Strutting for 
Shafts. 



METHODS OF HAULING IN TUNNELS 



59 



CHAPTER YL 
METHODS OF HAULING IN TUNNELS. 



The transportation from one point to another within the 
tunnel and its shafts of any material, whether it is excavated 
spoil or construction material, is defined as hauling. In all 
engineering construction, the transportation of excavated 
materials, and materials for construction, constitutes a very 
important part of the expense of the work; but hauling in 
tunnels where the room is very limited, and where work is 
constantly in progress over and at the sides of the track, is a 
particularly expensive process. Hauling in tunnels may be 
done either by way of the entrances, or by way of the shafts, 
or by way of both the entrances and shafts. 

Hauling by Way of Entrances. — When the hauling is done 
by the way of the entrances, the materials to be hauled are 
taken directly from the point 
of construction to the en- 
trances, or in the opposite di- 
rection, by means of special 
cars of different patterns. For 
general purposes, these differ- 
ent patterns of cars may be 
grouped into three classes, — 
platform-cars, dump-cars, and 
box-cars. Representative ex- 
amples of these several classes 

of cars are shown in Figs. 33 to 36 * inclusive, but it will be 
readily understood that there are many other forms. 

Briefly described, platform-cars (Fig. 33) consist of a 

* Reproduced from catalogue of Arthur Koppel, New York. 




Fig. S3 — Platform Car for Tunnel Work. 



60 



TUNNELING 




Fig. 34. — Iron Dump-Car for 
Tunnel Work. 



wooden platform mounted on tracks, and they are usually em- 
ployed for the transportation of timber, ties, etc. Dump-cars 
are used in greater numbers in tunnel work than any other 
form. Fig. 34 shows a dump-car of metal construction, and 

Fig. 35 one constructed with a metal 
under-frame and wooden box. Ihese 
cars are made to run on narrow-gauge 
tracks, and usually liave a capacity of 
about one to one and one-half cubic 
yards. Box-cars are more extensively 
employed in Europe for tunnel work 
than in Arnerica. Fig. 36 shows a 
typical European box-car for tunnel 
work. It is made either to run on narrow-gauge or standard- 
gauge tracks. 

It is usually desirable in tunnel work to employ cars of 
different forms for different parts of the work. hi rock 
tunnels it is a common practice to use narrow-gauge cars of 
small size in the headings, and 
larger, broad-gauge cars for the 
enlargement of the profile. 
Where narrow-gauge cars are 
employed for all purposes, it will 
also be found more convenient 
to use platform-cars for handling 
the construction material, and 
dump-cars for removing the spoil. 
The extent to which it is desir- 
able to use cars of different forms Fia. 35. -wooden nump-Car for Tunnel 

Work. 

will depend upon the character 

and conditions of the work, and particularly upon how far it is 

possible to install the permanent track. 

As a general rule, it is considered preferable to lay the 
permanent tracks at once, and do all the hauling upon them, 
so that as soon as the tunnel is completed, trains may pass 




METHODS OF HAULING IN TUNNELS 



61 



through without delay. To what extent this may be done, or 
whether it can be done at all or not, depends upon the method 
of excavation and other local conditions. In soft-ground 
tunnels excavated by the English or Austrian methods, 
it is quite possible to lay the permanent tracks at first, since 
the whole section is excavated at once, and the excavation is 
kept but a little ahead of the completed tunnel. In rock 
tunnels, where the heading is driven far ahead of the com- 
pleted section, it is, of course, impossible to keep the perma- 
nent track close to the advance work, and narrow-gauge tracks 
must be laid in the heading. The same thing is true in soft^ 
ground tunnels driven by successive headings and drifts. In 
these cases, therefore, 
where narrow-gauge 
tracks have to be used 
for some portions of 
the work anyway, the 
question comes up 
whether it is preferable 
to use temporary 
narrow-gauge tracks throughout, or to lay the permanent track 
as far ahead as possible, and then extend narrow-gauge tracks 
to the advance excavation. In the latter case it will, of course, 
be necessary to trans-ship each load from the narrow-gauge to 
the standard-gauge cars, or vice versa, which means extra cost 
and trouble. To avoid this, the method is sometimes adopted 
of laying a third rail between the standard-gauge rails, so that 
either standard- or narrow-gauge cars may be transported over 
the line. Whatever form the local conditions may require the 
system of construction tracks to assume, it may be set down as 
a general rule that the permanent tracks should be kept as far 
advanced as possible, and temporary tracks employed only 
where the permanent tracks are impracticable. 

The motive power employed for hauling in tunnels may be 
furnished by animals or by mechanical motors. Animal power 




Fig. 36. —Box-Car for Tunnel Work. 



62 TUNNELING 

is generally employed in short tunnels and in the advance 
headings and galleries. In long tunnels, or where the exca- 
vated material has to be transported some distance away from 
the tunnel, mechanical power is preferable, for obvious reasons. 
The motors most used are small steam locomotives, special 
compressed-air locomotives, and electric motors. Compressed 
air and electric locomotives are built in various forms, and are 
particularly well adapted for tunnel work because of their 
small dimensions, and freedom from smoke and heat. 

Hauling by Way of Shafts. — When the excavated material 
a-nd materials of construction are handled through shafts, the 
operation of hauling may be divided into three processes : 
the transportation of the materials along the floor of the 
tunnel, the hoisting of them through the shaft, and the sur- 
face transportation from and to the mouth of the shaft. These 
three operations should be arranged to work in harmony with 
each other, so as to avoid waste of time and unnecessary han- 
dling of the materials. An endeavor should be made to avoid, 
if possible, breaking or trans-shipping the load from the time 
it starts at the heading until it is dumped at the spoil bank. 
This can be accomplished in two ways. One way is to hoist 
the boxes of the cars from their trucks at the bottom of the 
shaft, and place them on similar trucks running on the surface 
tracks. The other way is to run the loaded cars on to the ele- 
vator platform at the bottom, hoist them, and then run them 
on to the surface tracks. If the first method is employed, the 
car box is usually made of metal, and is provided at its top 
edges with hooks or ears to which to attach the hoisting cables. 
When the second method is used, the elevator platform has 
tracks laid on it which connect with the tracks on the tunnel 
floor, and also with those on the surface. 

Hoisting Machinery. — The machines most commonly em- 
ployed for hoisting purposes in tunnel shafts are steam hoisting 
engines, horse gins, and windlasses operated by hand. Wind- 
lasses and horse gins are rather crude machines for hoisting 



METHODS OF HAULING IN TUNNELS 63 

loads, and are used only in special circumstances, where the 
shaft is of small depth, when the amount of material to be 
hoisted is small, or where for any reason the use of hoisting 
engines is precluded. The steam hoisting engine is the stan- 
dard machine for the rapid lifting of heavy vertical loads. 
Recently oil engines and electric hoists have also come to be 
used to some extent, and under certain conditions these ma- 
chines possess notable advantages. 

The construction of hand windlasses is familiar to every one. 
In tunnel work this device is located directly over the shaft, 
with its axis a little more than half a man's height, so that the 
crank handle does not rise above the shoulder line. To develop 
its greatest efficiency the hoisting rope is passed around the 
windlass drum so that the two ends hang down the shaft, and 
as one end descends the other ascends. A skip, or bucket, is 
attached to each of the rope ends ; and by loading the descend- 
ing skip with construction materials and the ascending skip 
with spoil, the two skip loads tend to balance each other, thus 
increasing the capacity of the windlass, and decreasing the 
manual labor required to operate it. Skips varying from 0.3 
cu. yd. to 0.5 cu. yd. are used. The horse gin consists of a 
vertical cylinder or drum provided with radial arms to which 
the horses are hitched, which revolve the cylinder by walking 
around it in a circle. The hoisting rope is rove around the 
drum so that the two ends extend down the shaft with skips 
attached, as described in speaking of the hand windlass. The 
power of the horse gin is, of course, much greater than that of a 
windlass operated by hand, skips of 1 cu. yd. capacity being 
commonly used. Horse gins are no longer economical hoisting 
machines, according to one prominent authority, when V 
(HH-20) > 5000, where V equals the volume of material to 
be hoisted, and H equals the height of the hoist, the weight of 
the excavated material being 2100 lbs. per cu. yd. As a gen- 
eral rule, however, it is assumed that it is not economical to 
employ horse gins with a depth of shaft exceeding 150 ft. 



64 TUNNELING 

As already stated, the most efficient and most commonly 
used device for hoisting at tunnel shafts is the steam hoisting 
engine. There are numerous builders of hoisting engines, each 
of which manufactures several patterns and sizes of engines. 
In each case, however, the apparatus consists of a boiler supply- 
ing steam to a horizontal engine which operates one or more 
rope drums. The engines are always reversible. They may 
be employed to hoist the skips directly, or to operate elevators 
upon which the skips or cars are loaded. In either case the 
hoisting ropes pass from the engine drum to and around ver- 
tical sheaves situated directly over the shaft so as to secure the 
necessary vertical travel of the ropes down the shaft. Where 
the shaft is divided into two compartments, each having an ele- 
vator or hoist, double-drum engines are employed, one drum 
being used for the operations in one compartment, and the other 
for the operations in the other compartment. Where the work 
is to be of considerable duration, or when it is done in cold 
weather, more or less elaborate shelters or engine houses are 
built to cover and protect the machinery. 

Choice between the method of hoisting the skips directly, 
and the method of using elevators, depends upon the extent and 
character of the work. Where large quantities of material are 
to be hoisted rapidly, it is generally considered preferable to 
employ elevators instead of hoisting the skips directly. In 
direct hoisting at high speed, oscillations are likely to be pro- 
duced which may dash the skips against the sides of the shaft 
and cause accidents. The loads which can be carried in single 
skips are also smaller than those possible where elevators are 
used ; and this, combined with the slower hoisting speed required, 
reduces the capacity of this method, as compared with the use 
of elevators. Where elevators are employed, however, the plant 
required is much more extensive and costly ; it comprising not 
only the elevator cars with their safety devices, etc., but the 
construction of a guiding framework for these cars in the tun- 
nel shaft. For these various reasons the elevator becomes the 



METHODS OF HAULING IN TUNNELS 



65 



preferable hoisting device where the quantity of material to be 
handled is large, where the shafts are deep, and where the work 
will extend over a long period of time ; but when the contrary 
conditions are the case, direct hoisting of the skips is generally 
the cheaper. The engineer has to integrate the various factors 
in each individual case, and 
determine which method will 
best fulfill his purpose, which 
is to handle the material at 
the least cost within the 
given time and conditions. 
The construction of ele- 
vators for tunnel work is 
simple. The elevator car 
consists usually of an open 
framework box of timber and 
iron, having a plank floor on 
which car tracks are laid, 
and its roof arranged for 
connecting the hoisting cable 
(Fig. 37 *). Rigid construc- 
tion is necessary to resist the 
hoisting strains. The sides 
of the car are usually de- 
signed to slide against tim- 
ber guides on the shaft walls. 
Some form of safety device, 
of which there are several kinds, should be employed to pre- 
vent the fall of the elevator, in case the hoisting rope breaks, 
or some mishap occurs to the hoisting machinery, which en- 
dangers the fall of the car. Speaking tubes and electric-bell 
signals should also be provided to secure communication be- 
tween the top and bottom of the shaft. 

* Reproduced from the catalogue of the Ledgerwood Manufacturing Company, New 
York. 




Fig. 37, — Elevator Car for Tunnel Shafts. 



66 



TUNNELING 



CHAPTER VII. 

TYPES OF CENTERS AND MOLDS EMPLOYED 

IN CONSTRUCTING TUNNEL LININGS 

OF MASONRY. 



The masonry lining of a tunnel may be describea as con- 
sisting of two or more segments of circular arches combined 
so as to form a continuous solid ring of masonry. To direct 
the operations of the masons in constructing this masonry 
ring, templates or patterns are provided which show the exact 
dimensions and form of the sectional profile which it is de- 
sired to secure. These patterns or templates will vary in 
number and construction with the form of lining and the 
method of excavation adopted. Where the excavation is fully 
lined on all four sides, the masonry work is usually divided 
into three parts, — the invert or floor masonry, the side-wall 
masonry, and the roof-arch masonry. At least one separate 
pattern has to be employed in constructing each of these parts 
of the lining; and they are known respectively as ground 
molds, leading frames, and arch centers, or simply centers. In 
the following paragraphs the form and construction usually 
employed for each of these three kinds of patterns is de- 
scribed. 

Ground Molds. — Ground molds are employed in building the 
tunnel invert. They are generally constructed of 3-inch plank 
cut exactly to the form and dimensions of the invert masonry 
as shown in Fig. 38. To permit of convenience of handling in 
a restricted space, they are generally made in two parts, which 
are joined at the middle by means of iron fish-plates and bolts. 
Either one or two ground molds may be employed. Where two 



TYPES OF CENTERS AND MOLDS 



Q7 




Fig. 38. — Ground Mold for Constructing 
Tunnel Invert Masonry. 



molds are used they are set up a short distance apart, and cords 
are stretched from one to the other parallel to the axis of the 
tunnel, by which the masons are guided in their work. Ex- 
treme care has to be taken in 
setting the molds to ensure that 
they are fixed at the proper 
grade, and are in a plane normal 
to the axis of the tunnel. Where 
only one ground mold is employed, the finished masonry is 
depended upon to supply the place of the second mold, cords 
being stretched from it to the single mold placed the requisite 
distance ahead. The leveling and centering of the molds is ac- 
complished by means of transit and level. 

Two modifications of the form of ground mold shown by 
Fig. 39 are employed. The first modification is peculiar to 

the English method of 
excavation, and consists 
in combining the ground 
mold with the leading 
frame for the lower part 
of the side walls, as 
shown by Fig. 39. The 
second modification is 
employed where the two 
halves or sides of the 
invert are built separately, and it consists simply in using one- 
half of the mold shown by Fig. 38. When the last method of 
constructing the invert masonry is resorted to, extreme care has 
to be observed in setting the half-mold in order to avoid error. 

Leading Frames. — As already stated, leading frames are the 
patterns, or molds, used in building the side walls of the lining. 
Like the ground mold they are usually built of plank ; one 
side being cut to the curve of the profile, and the other being 
made parallel to the vertical axis of the tunnel section. The 
vertical side usually has some arrangement by which a plumb 




Fig. 39. — Combined Ground Mold and Leading Frame 
for Invert and Side Wall Masonry. 



68 



TUNNELING 




bob can be attached, as shown by Fig. 40, to guide the work> 
men in erecting the frame. The combined leading frame and 
ground mold shown in Fig. 39 has already been described. 
The use of this frame is possible only where the 
masonry is begun at the invert and carried up on 
each side at the same time. This mode of con- 
struction is peculiar to the English method of 
tunneling; in all other methods the form of sep- 
arate ground frame shown by Fig. 40 is employed. 
Fig. 40.— Lead- 'pj-^g gfround frames are lined in and leveled up bv 

mg Frame for ° r j 

Constructing transit and level ; and, as in setting the ground 

Side Wall Ma- /. j i j i j^ 

sonry. iramcs, care must be taken to secure accuracy m 

both direction and elevation. 

Arch Centers. — The template or form upon which the roof 
arch is built is called a center. Unlike the ground molds and 
leading frames, the arch centers have to support the weight of 
the masonry and the roof pressures during the construction of 
the lining, and they, therefore, require to be made strong. 
Owing to the fact that the pressures are indeterminate, it is 
impossible to design a rational center, and resort is had to those 
constructions which past experience has shown to work satis- 
factorily under similar conditions. In a general way it can 
always be assumed that the construction should be as simple 
as possible, that the center should be so designed that it can 
be set up and removed with the least possible labor, and that 
the different pieces of the framework and lagging should be as 
short as possible, for convenience in handling. 

Tunnel centers are usually composed of two parts, — a mold 
or curved surface upon which the masonry rests, and a frame- 
work which supports the mold. The curved surface or mold 
consists of a lagging of narrow boards running parallel to the 
tunnel axis, which rests upon the arched top members of two 
or more consecutive supporting frames. The supporting frame 
is built in the form of a truss, and must be made strong enough 
to withstand the heavy superimposed loads, consisting of the 



TYPES OF CENTERS AND MOLDS 69 

arch masonry during construction, and of the roof pressures 
which are transferred to the center when the strutting is 
removed to allow the masonry to be placed. The framework 
of the center is supported either by posts resting upon the floor 
of the excavation, or upon the invert masonry when this is 
built first, as in the Enghsh and Austrian methods, or it may 
be supported directly upon the ground where the arch masonry 
is built first, as in the Belgian method of tunneling. 

In describing the various methods of tunneling in succeed- 
ing chapters, the center construction and method of supporting 
the center peculiar to each will be fully explained, and only a 
few general remarks are necessary here. Centers may be classi- 
fied according to their construction and composition into plank 
centers, truss centers, and iron centers. 

One of the most common forms of plank centers is shown 
by Fig. 41. It consists of two 
half-polygons whose sides consist 
of 15 in. X 4 ft. planks having 
radial end-joints. These two half- 
polygons are laid one upon the 
other so that they break joints, as 

shown by the figure, and the ex- Fig. 4l.-Plank center for Construct- 

•^ . ing the Roof Arch. 

trados of the frame is cut to the 

true curve of the roof arch. The planks commonly used for 
making these centers are 4 ins. thick, making the total thick- 
ness of the center 8 ins. Plank centers of the construction 
described are suitable only for work where the pressures to be 
resisted are small, as in tunnels through a fairly firm rock, al- 
though there have been instances of their successful use in soft- 
ground tunnels. 

Where heavy loads have to be carried, trussed centers are 
generally employed, the trusses being composed of heavy square 
beams with scarfed and tenoned joints, reinforced by iron plates. 
Different forms of trusses are employed in each of the differ- 
ent methods of tunneling, and each of these is described in sue- 




70 



TUNNELING 




Fig. 42.— Trussed Center for Constructing] 
the Eoof Arch. 



ceeding chapters ; but they are generally either of the king-post 
or queen-post type, or some modification of them. The king- 
post truss may be used alone, with 
or without the tie-beam, as shown 
by Fig. 42 ; but generally a queen - 
post truss is made to form the 
base of support for a smaller king 
post truss mounted on its top. 
This arrangement gives a trape- 
zoidal form to the center, which approaches closely to the arch 
profile. Owing to the character of the pressures transmitted to 
the center, the usual tension members can be made very light. 

The combined center and strutting system devised by Mr. 
Rziha has already been described in a previous chapter. In 
recent European tunnel work quite extensive use has also been 
made of iron centers consisting of several segments of curved 
I-beams, connected by fish-plate joints so as to form a semi- 
circular arch rib. The ends or feet of these I-beam ribs have 
bearing-plates or shoes made by riveting angles to the I-beams. 
Centers constructed in a similar manner, but made of sections 
of old railway rail, were used in carrying out the tunnel work 
on the Rhine River Railroad in Germany. The advantages 
claimed for iron centers are that they take up less room, and 
that they can be used over and over again. 

Setting Up Centers. — According to the method of excava- 
tion followed in building the tunnel, the centers for building 
the roof arch may have to be supported by posts resting on the 
tunnel floor ; or where the arch is built first, as in the Belgian 
and Italian methods, they may be carried on blocking resting 
on the unexcavated earth below. Whichever method is em- 
ployed, an unyielding support is essential, and care must be 
taken that the centers are erected and maintained in a plane 
normal to the tunnel axis. To prevent deflection and twisting, 
the consecutive centers are usually braced together by longi- 
tudinal struts or by braces running to the adjacent strutting. 



TYPES OF CENTERS AND MOLDS 71 

Only skilled and experienced workmen should be employed in 
erecting the centers ; and they should work under the immedi- 
ate direction of the engineer, who must establish the axis and 
level of each center by transit and level. 

Lagging, — By the lagging is meant the covering of narrow 
longitudinal boards resting upon the upper curved chords of the 
centers, and spanning the opening between consecutive centers. 
This lagging forms the curved surface or mold upon which the 
arch masonry is laid. When the roof arch is of ashlar masonry 
the strips of lagging are seldom placed nearer together than 
the joints of the consecutive ring stones, but in brick arches 
they are laid close together. Besides the weight of the arch 
masonry, the lagging timbers support the short props which 
keep the pohng-boards in place after the strutting is removed 
and until the arch masonry is completed. 

Striking the Centers. — The centers are usually brought to 
the proper elevation by means of wooden wedges inserted be- 
tween the sill of the center and its support, or between the 
bottom of the posts carrying the center and the tunnel floor. 
These wedges are usually made of hard wood, and are about 
6 ins. wide by 4 ins. thick by 18 ins. long. To strike the center 
after the arch masonry is completed, these wedges are with- 
drawn, thus allowing the center to fall clear of the masonry. 
Usually the center is not removed immediately after striking, 
so that if the arch masonry fails the ruins will remain upon the 
center. The method of striking the iron center devised by Mr. 
Rziha has been described in the previous chapter on strutting. 



TUNNELING 



CHAPTER VIII. 
METHODS OF LINING TUNNELS, 



Tunnels in soft soils and in loose rock, and rock liable to 
disintegration, are always provided with a lining to hold the 
walls and roof in place. This lining may cover the entire 
sectional profile of the tunnel, or only a part of it, and it may 
be constructed of timber, iron, iron and masonry, or, more 
commonly, of masonry alone. 

Timber Lining. — Timber is seldom employed in lining 
tunnels except as a temporary expedient, and is replaced by 
masonry as soon as circumstances will permit. In the first 
construction of many American railways, the necessity for 
extreme economy in construction, and of getting the line open 
for traffic as soon as possible, caused the engineers to line 
many tunnels with timber, which was plentiful and cheap. 
Except for their small cost and the ease and rapidity with 
which they can be constructed, however, these timber linings 
possess few advantages. It is only the matter of a few years 
when the decay of the timber makes it necessary to rebuild 
them, and there is always the serious danger of fire. In 
several instances timber-lined tunnels in America have been 
burned out, causing serious delays in traffic, and necessitating 
complete reconstruction. Usually this reconstruction has con- 
sisted in substituting masonry in place of the original timber 
lining. In a succeeding chapter a description will be given of 
some of the methods employed in replacing timber tunnel 
linings with masonry. Various forms of timber lining are 
employed, of which Fig. 44 and the illustrations in the chapter 



METHODS OF LINING TUNNELS 



73 



discussing the methods of relining timber-lined tunnels with 
masonry are typical examples. 

Iron Lining. — The use of iron lining for tunnels was intro- 
duced first on a large scale by Mr. Peter William Barlow in 
1869, for the second tunnel under the River Thames at 
London, England, and it has greatly extended since that time. 
The lining of the second Thames tunnel consisted of cylindrical 
cast-iron rings 8 ft. in diameter, the abutting edges of the 
successive rings being flanged and provided with holes for 
bolt fastenings. Each ring was made up of four segments, 




Cross ^Section. Longitudinal Section, 

Figs. 43 and 44. — A Typical Form of Timber Lining for Tunnela. 

three of which were longer than quadrants, and one much 
smaller forming the " key-stone " or closing piece. These 
segments were connected to each other by flanges and bolts. 
To make the joints tight, strips of pine or cement and hemp 
yarn were inserted between the flanges. Since the construc- 
tion of the second Thames tunnel, iron lining has been em- 
ployed for a great many submarine tunnels in England, 
Continental Europe, and America, some of them having a 
section over 28 ft. in diameter. Where circular iron lining is 
employed, the bottom part of the section is leveled up with 
concrete or brick masonry to carry the tracks, and the whole 



74 TUNNELING 

interior of the ring is covered with a cement plaster lining 
deep enough thoroughly to embed the interior joint flanges. 
In the succeeding chapter describing the methods of driving 
tunnels by shields several forms of iron tunnel lining are fully 
described. 

Iron and Masonry Lining. — During recent years a form of 
combined masonry and iron lining has been extensively em- 
ployed in constructing city underground railways in both 
Europe and America. Generally this form of lining is built 
with a rectangular section. Two types of construction are 
employed. In the first, masonry side walls carry a flat roof 
of girders and beams, which carry a trough flooring filled with 
concrete, or between which are sprung concrete or brick arches. 
Sometimes the roof framing consists of a series of parallel 
I-beams laid transversely across the tunnel, and in other cases 
transverse plate girders carry longitudinal I-beams. In the 
second type of construction the roof girders are supported by 
columns embedded in the side walls. Where the tunnel pro- 
vides for two or four tracks, intermediate column supports are 
in some cases introduced between the side columns. In this 
construction the roofing consists of concrete filled troughs or of 
concrete or brick arches, as in the construction first described. 
Examples of combined masonry and iron tunnel lining are 
illustrated in the succeeding chapter on tunneling under city 
streets. 

Masonry Lining. — The form of tunnel lining most commonly 
employed is brick or stone masonry. Concrete and reinforced 
concrete masonry lining has been employed in several tunnels 
built in recent years. The masonry lining may inclose the whole 
section or only a part of it. The floor or invert is the part most 
commonly omitted ; but sometimes also the side walls and invert 
are both omitted, and the lining is confined simply to an arch 
supporting the roof. The roof arcn, the side wafls, and the invert 
compose the tunnel lining; and all three may consist of stone or 
brick alone, or stone side walls may be employed with brick invert 



METHODS OF LINING TUNNELS 75 

and roof arch. Rubble-stone masonry is usually employed, 
except at the entrances, where tUe masonry is exposed to view. 
Here ashlar masonry is usually used. The stone selected for 
tunnel lining should be of a durable quality which weathers 
well. Where bricks are used they should be of good qual- 
ity. Owing to the comparative ease with which brick arches 
can be built, they are generally used to form the roof arch, even 
where the side walls are of stone masonry. Masonry lining 
may be built in the form of a series of separate rings, or in the 
form of a continuous structure extending from one end of the 
tunnel to the other. The latter method of construction pro- 
duces a stronger structure ; but in case of failure by crush- 
ing, the damage done is hkely to be more widespread than 
where separate rings are employed, one or two of which 
may fail without injury to the others adjacent to them. The 
construction is also somewhat simpler where separate rings are 
employed, since no provision has to be made for bonding the 
whole lining into a continuous structure. Where a series of 
separate rings is employed, the length of each ring runs from 
5 ft. up to 20 ft., it depending upon the character of the 
material penetrated, and the method of construction employed. 
For the purpose of detailed discussion the construction of 
masonry lining may be divided into four parts, — the side-wall 
foundations, the side walls themselves, the roof arch, and the 
invert. 

Concrete and reinforced concrete linings are now extensively 
used on account of cheapness and facility of handhng, but they 
have the great disadvantage of resisting pressure after they 
become hard, which is some time after being placed. The 
strutting should, therefore, be left to support the roof so as to 
prevent direct pressure on the fresh material. The roof, as a 
rule, is supported by longitudinal planks held in position by 
five or seven segments of arched frames placed across the tunnel. 
A large quantity of timber and carpenter work is thus entirely 
wasted and these costly items, in many cases, make the concrete 



76 TUNNELING 

lining of a tunnel more expensive than the one built of brick 
and stone. To avoid these inconveniences tunnels have been 
successfully lined with concrete on the side walls and concrete 
blocks in the arches. These blocks have been built by hand 
and molded in the shape of the arch voussoirs. 

Foundations. — In tunnels through rock of a hard and dur- 
able character the foundations for the side walls are usually 
laid directly on the rock. In loose rock, or rock Hable to dis- 
integration, this method of construction is not generally a safe 
one, and the foundation excavation should be sunk to a depth 
at which the atmospheric influences cannot affect the founda- 
tion bed. In either case the foundation masonry is made 
thicker than that of the side walls proper, so as to distribute 
the pressure over a greater area, and to afford more room for 
adjusting the side-wall masonry to the proper profile. In 
yielding soils a special foundation bed has to be prepared for 
the foundation masonry. In some instances it is found suffi- 
cient to lay a course of planks upon which the masonry is con- 
structed, but a more sohd construction is usually preferred. 
This is obtained by placing a concrete foot- 
ing from 1 ft. to 2 ft. deep all along the 
bottom of the foundation trench, or in some 
cases by sinking wells at intervals along the 
trench and filling them with concrete, so as 
to form a series of supporting pillars. 

The form given to the foundation courses 
^. and lower portions of the side walls varies. 

Fig. 45. — Diagram ^ 

Showing Forms Where a large bearing area is required, the 

Adopted for Side- i i p xi n • • i <• n 

Wall Foundations. back of the Wall IS carried up vertically as 
shown by the fine AB, Fig. 45, otherwise the 
rear face of the wall follows the line of excavation AC. For 
similar reasons the front face of the wall may be made vertical, 
as at FG, or inclined, as at FH. The line FE indicates the shelf 
construction designed to support the feet of the posts used to 
carry the arch centers during the construction of the roof arch. 




METHODS OF LINING TUNNELS 77 

Side Walls. — The construction of the side walls above the 
foundation courses is carried out as any similar piece of masonry 
elsewhere would be built. To direct the work and insure 
that the inner faces of the walls follow accurately the curve 
of the chosen profile, leading frames previously described are 
employed. 

Roof Arch. — For the construction of the roof arch, the 
centers previously described are employed. Beginning at the 
edges of the center on each side, the masonry is carried up a 
course at a time, care being taken to have it progress at the 
same rate on both sides, so that the load brought onto the 
centering is symmetrical. As soon as the centers are erected, 
the roof strutting is removed, and replaced by short props 
which rest on the lagging of the centers and support the poling- 
boards. These props are removed in succession as the arch 
masonry rises along the curve of the center, and the space 
between the top of the arch masonry and the ceiling of the 
excavation is filled with small stones packed closely. The key- 
stone section of the arch is built last, by inserting the stones or 
bricks from the front edge of the arch ring, there being no room 
to set them in from the top, as is the practice in ordinary open- 
arch construction. The keying of the arch is an especially 
difficult operation, and only experienced men skilled in the 
work should be employed to perform it. The task becomes 
one of unusual difficulty when it becomes necessary to join the 
arches coming from opposite directions. 

Invert. — In all but one or two methods of tunneling, the 
invert is the last portion of the lining to be built. In the EngHsh 
method of tunneling, the invert is the first portion of the hning 
to be built, and the same practice is sometimes necessary in 
soft soils where there is danger of the bottoms of the side walls 
being squeezed together by the lateral pressures unless the 
invert masonry is in place to hold them apart. The ground 
molds previously described are employed to direct the con- 
struction of the invert masonry. 



78 TUNNELING 

General Observations. — In describing the construction of the 
roof arch, mention was made of the stone filling employed 
between the back of the masonry ring and the ceiling of the 
excavation. The spaces behind the side walls are filled in a 
similar manner. The object of this stone filling, which should 
be closely packed, is to distribute the vertical and lateral pres- 
sures in the walls of the excavation uniformly over the lining 
masonry. As the masonry work progresses, the strutting em- 
ployed previously to support the w^alls of the excavation has 
to be removed. This work requires care to prevent accident, 
and should be placed in charge of experienced mechanics who 
are familiar with its construction, and can remove it with the 
least damage to the timbers, so that they may be used again, 
and without causing the fall of the roof or the caving of the 
sides by removing too great a portion of the timbers at one 
time. 

Thickness of Lining Masonry. — It is obvious, of course, that 
the masonry lining must be thick enough to support the pres- 
sure of the earth which it sustains; but, as it is impossible to 
estimate these pressures at all accurately, it is difficult to say 
definitely just what thickness is required in any individual case. 
Rankine gives the following formulas for determining the depths 
of keystone required in different soils : 
For firm soils 



= \/o.l2-, 



and for soft soils. 



.^. 



y,2 

48-, 



where d = the depth of the crown in feet, r = the rise of the 
arch in feet, and s = the span of the arch in feet. Other writers, 
among them Professor Curioni, attempt to give rational methods 
for calculating the thickness of tunnel fining; but they are 
all open to objection because of the amount of hypothesis re- 



METHODS OP LINING TUNNELS 



79 



quired concerning pressures which are of necessity indetermi- 
nate. Therefore, to avoid tedious and uncertain calculations, 
the engineer adopts dimensions which experience has proven to 
be ample under similar conditions in the past. Thus we have 
all gradations in thickness, from hard-rock tunnels requiring 
no lining, and tunnels through rocks which simply require a 
thin shell to protect them from the atmosphere, to soft-ground 
tunnels where a masonry lining 3 ft. or more in thickness is 
employed. Table II. shows the thickness of masonry lining 
used in tunnels through soft soils of various kinds. 

The thickness of the masonry lining is seldom uniform at 
all points, as is indicated by Table II. Figs. 46 and 47 show 
common methods of varying the thickness of lining at different 
points, and are self-explanatory. 




Figs. 46 and 47. — Transverse Sections of Tunnels Showing Methods of Increasing the Thick- 
ness of the Lining at Different Points. 



Side Tunnels. — When tunnels are excavated by shafts located 
at one side of the center line, short side tunnels or galleries are 
built to connect the bottoms of the shafts with the tunnel proper. 
These side tunnels are usually from 30 ft. to 40 ft. long, and 
are generally made from 12 ft. to 14 ft. high, and about 10 ft. 
wide. The excavation, strutting, and lining of these side tun- 
nels are carried on exactly as they are in the main tunnel, with 



80 



TUNNELING 



such exceptions as these short lengths make possible. Table 
III. gives the thickness of lining used for side tunnels, the 
figures being taken from European practice. 

Culverts. — The purpose of culverts in tunnels is to collect 
the water which seeps into the tunnel from the walls and shafts. 
The culvert is usually located along the center line of the tunnel 
at the bottom. In soft-ground tunnels it is built of masonry, 
and forms a part of the invert, but in rock tunnels it is the 
common practice to cut a channel in the rock floor of the excava- 
tion. Both box and arch sections are employed for culverts. 
The dimensions of the section vary, of course, with the amount 
of water which has to be carried away. The following are the 
dimensions commonly employed: 



Kind of Culvkrt. 


Height in 

Feet. 


Width in 
Feet. 


Thickness of 

Walls in 

Feet. 


Thickness of 

Covering in 

Feet. 


Box culvert .... 
Arch culvert . . . 


1 to 1.5 
1 to 1.5 


1 to 1.5 
1 to 1.5 


0.8tol.2 
0.8 to 1.2 


0.3 
0.4 



It should be understood that the dimensions given in the 
table are those for ordinary conditions of leakage; where larger 
quantities of water are met with, the size of the culverts has, 
of course, to be enlarged. To permit the water to enter the 
culvert, openings are provided at intervals along its side; and 
these openings are usually provided with screens of loose stones 
which check the current, and cause the suspended material to 
be deposited before it enters the culvert. In cases where springs 
are encountered in excavating the tunnel, it is necessary to 
make special provisions for confining their outflow and con- 
ducting it to the culvert. In all cases the culverts should be 
provided with catch basins at intervals of from 150 ft. to 300 
ft., in which such suspended matter as enters the culverts is 
deposited, and removed through covered openings over each 
basin. At the ends of the tunnel the culvert is usually divided 



METHODS OF LINING TUNNELS 



81 



into two branches, one running to tlie drain on each side of the 
track. 

Niches. — In short tunnels niches are employed simply as 
places of refuge for trackmen and others during the passing of 
trains, and are of small size. In long tunnels they are made 



1.,^ 





Fig, 48. — Refuge Niche in St. Gothard Tunnel. 

larger, and are also employed as places for storing small tools 
and supplies employed in the maintenance of the tunnel. Niches 
are simply arched recesses built into the sides of the tunnel, 
and lined with masonry; Fig. 48 shows this construction quite 
clearly. Small refuge niches are usually built from 6 ft. to 
9 ft. high, from 3 ft. to 6 ft. wide, and from 2 ft. to 3 ft. deep. 
Large niches designed for storing tools and supplies are made 
from 10 ft. to 12 ft. high, from 8 ft. to 10 ft. wide, and from 
18 ft. to 24 ft. deep, and are provided with doors. Refuge 
niches are usually spaced from 60 ft. to 100 ft. apart, while 
the larger storage niches may be located as far as 3000 ft. apart. 
The niche construction shown by Fig. 48 is that employed on 
the St. Gothard tunnel. 

Entrances. — The entrances, or portals, of tunnels usually 
consist of more or less elaborate masonry structures, depending 
upon the nature of the material penetrated. In soft-ground 
tunnels extensive wing walls are often required to support the 
earth above and at the sides of the entrance; while in tunnels 
through rock, only a masonry portal is required, to give a finish 
to the work. Often the engineer indulges himself in an elabo- 
rate architectural design for the portal masonry. There is 



82 



TUNNELING 



danger of carrying such designs too far for good taste unJess 
care is employed; and on this matter the writer can do no better 




Fig. 49. — East Portal of Hoosac Tunnel. 

than to quote the remarks of the late Mr. Frederick W. Simms 
in his well-known '' Practical Tunneling ": 

"The designs for such constructions should be massive to be suitable as 
approaches to works presenting the appearance of gloom, solidity, and 
strength. A light and highly decorated structure, however elegant and well 
adapted for other purposes, would be. very unsuitable in such a situation; it 
is plainness combined with boldness, and massiveness without heaviness, 
that in a tunnel entrance constitutes elegance, and, at the same time, is the 
most economical." 

Fig. 49 is an engraving from a photograph of the east portal 
of the Hoosac tunnel, which is an especially good design. The 
portals of the Mount Cenis tunnel were built of samples of 
stone encountered all along the line of excavation. The stones 
were cut and dressed and utilized for walls and voussoirs. The 
only ornament that is usually allowed on the portals is the date 
of the opening of the tunnel prominently cut in the stone above 
the arch. 



METHODS OF LINING TUNNELS 



8a 



TABLE n. 
Showing Thickness of Masonry Lining for Tunnels through Soft Ground. 



Character of Material. 


Keystone. 


Springers . 


Invert. 


Laminated clay, first variety. . 
Laminated clay, second variety 
Laminated clay, third variety . 
Quicksand 


Ft. 

2. 15 to 3 
3 to 4.5 
4.5 to 6.5 
2 to 3.28 


Ft. 

2.75 to 3.5 
3.5 to5.5 
5.5 to8.1 
2 to 4.1 


Ft. 

1.6 to2.5 
2.5 to 4 
4 to 4.5 
1.33 to 2.5 



TABLE m. 

Showing Thickness of Masonry Lining for Side Tunnels through 
Soft Ground. 



Character op Material. 



Laminated clay, first variety. . 
Laminated clay, second variety 
Laminated clay, third variety . 
Quicksand 



Keystone. 



Ft. 

1.6to2.3 
2.3 to 3 
3 to 4 
1.6 to 2.5 



Springers. 



Ft. 

1.8 to 3 
3 to 4, 
4.1 to 5 
1.3 to 2 



Invert. 



Ft. 

1.5to2 
2 to 2.6 
2.6 to 3.29 
1.3 to 2 



84 TUNNELING 



CHAPTER IX. 

TUNNELS THROUGH HARD ROCK; GENERAL 

DISCUSSION; REPRESENTATIVE MECHANICAL 

INSTALLATIONS FOR TUNNEL WORK. 



The present high development of labor-saving machinery 
for excavating rock makes this material one of the safest and 
easiest to tunnel of any with which the engineer ordinarily has 
to deal. To operate this machinery requires, however, the 
developifient of a large amount of power, its transmission to 
considerable distances, and, finally, its economical application 
to the excavating tools. The standard rock excavating ma- 
chine is the power drill, which requires either air or hydraulic 
pressure for its operation according to the special type em- 
ployed. Under present conditions, therefore, the engineer is 
limited either to air or water under compression for the trans- 
mission of his power. Steam-power may be employed directly 
to operate percussion rock drills ; but owing to the heat and 
humidity which it generates in the confined space where the 
drills work, and because of other reasons, it is seldom employed 
directly. Electric transmission, which offers so many advan- 
tages to the tunnel builder, in most respects is largely excluded 
from use by the failure which has so far followed all attempts 
to apply it to the operation of rock drills. As matters stand, 
therefore, the tunnel engineer is practically limited to steam 
and falling water for the generation of power, and to com- 
pressed air and hydraulic pressure for its transmission. 

Whether the engineer should adopt water-power or steam to 
generate the power required for his excavating machinery de- 
pends upon their relative availability, cost, and suitability to the 



TUNKELS THROUGH HARD ROCK 85 

conditions of work in each particular case. Where fuel is plen- 
tiful and cheap, and where water-power is not available at a 
comparatively reasonable cost, steam-power will nearly always 
prove the more economical ; where, however, the reverse con- 
ditions exist, which is usually the case in a mountainous 
country far from the coal regions, and inadequately supplied 
with transportation facilities, but rich in mountain torrents, 
water-power will generally be the more economical. In a suc- 
ceeding chapter the power generating and transmission plants 
for a number of rock tunnels are described, and here only a 
general consideration of the subject will be presented. 

Steam-Power Plant. — A steam-power plant for tunnel work 
should be much the same as a similar plant elsewhere, except 
that in designing it the temporary character of its work must 
be taken into consideration. This circumstance of its tempo- 
rary employment prompts the omission of all construction 
except that necessary to the economical working of the plant 
during the period when its operation is required. The power- 
house, the foundations for the machinery, and the general con- 
struction and arrangement, should be the least expensive which 
will satisfy the requirements of economical and safe operation 
for the time required. It will often be found more economical 
as a whole to operate the machinery with some loss of economy 
during the short time that it is in use than to go to much 
greater expense to secure better economy from the machinery 
by design and construction, which will be of no further use 
after the tunnel is completed. The longer the plant is to be 
required, the nearer the construction may economically approach 
that of a permanent plant. As regards the machinery itself, 
whose further usefulness is not limited by the duration of any 
single piece of work, true economy always dictates the purchase 
of the best quality. Speaking in a general way, a steam-power 
plant for tunnel work comprises a boiler plant, a plant of air 
compressors with their receivers, and an electric light dynamo. 
When hydraulic transmission of power is employed, the air 



86 TUNNELING 

compressors are replaced by high-pressure pumps ; and when 
electric hauling is employed, one or more dynamos may be re- 
quired to generate electricity for power purposes, as well as for 
lighting. In addition to the power generating machines proper, 
there must be the necessary piping and wiring for transmitting 
this power, and, of course, the equipment of drills and other 
machines for doing the actual excavating, hauling, etc. 

Reservoirs. — When water-power is employed, a reservoir 
has to be formed by damming some near-by mountain stream at 
a point as high as practicable above the tunnel. The provision 
of a reservoir, instead of drawing the water directly from the 
stream, serves two important purposes. It insures a continuous 
supply and constant head of water in case of drought, and also 
permits the water to deposit its sediment before it is delivered 
to the turbines. The construction of these reservoirs may be 
of a temporary character, or they may be made permanent 
structures, and utilized after construction is completed to sup- 
ply power for ventilation and other necessary purposes. In the 
first case they are usually destroyed after construction is fin- 
ished. In either case, it is almost unnecessary to say, they 
should be built amply safe and strong according to good engi- 
neering practice in such works, for the duration of time which 
they are expected to exist. 

Canals and Pipe Lines. — For conveying the water from the 
reservoirs to the turbines, canals or pipe lines are employed. 
The latter form of conduit is generally preferable, it being 
both less expensive and more easily constructed than the 
former. It is advisable also to have duplicate lines of pipe to 
reduce the possibility of delay by accident or while necessary 
repairs are being made to one of the pipes. The pipe lines 
terminate in a penstock leading into the turbine chamber, and 
provided with the necessary valves for controlling the admis- 
sion of water to the turbines. 

Turbines. — There are numerous forms of turbines on the 
market, but they may all be classed either as impulse turbines 



TUNNELS THKOUGH HAKD PvOCK 87 

or as reaction turbines. Impulse turbines are those in which 
the whole available energy of the water is converted into 
kinetic energy before the water acts on the moving part of the 
turbine, lieaction turbines are those in which only a part of 
the available energy of the water is converted into kinetic 
energy before the water acts on the moving vanes. Impulse 
turbines give efficient results with any head and quantity of 
water, but they give better results when the quantity of water 
varies and the head remains constant. Reaction turbines, on 
the contrary, give better results when the quantity of water 
remains constant and the head varies. These observations 
indicate in a general way the form of turbine which will best 
meet the particular conditions in each case. The number of 
turbines required, and their dimensions, will be determined in 
each case by the number of horse-power required and the 
quantity of water available. The power of the turbines is 
transmitted to the air compressors or pumps by shafting and 
gearing. 

Air Compressors. — An air compressor is a machine — usually 
driven by steam, although any other power may be used — by 
which air is compressed into a receiver from which it may be 
piped for use. For a detailed description of the various forms 
of air compressors the reader should consult the catalogues of 
the several makers and the various text-books relating to air 
compression and compressed air. Air compressors, like other 
machines, suffer a loss of power by friction. The greatest loss 
of power, however, results from the heat of compression. 
When air is compressed, it is heated, and its relative volume 
is increased. Therefore, a cubic foot of hot air in the com- 
pressor cylinder, at say, 60 lbs. pressure, does not make a cubic 
foot of air at 60 lbs. pressure after cooling in the receiver. 
In other words, assuming pressure to be constant, a loss of 
volume results due to the extraction of the heat of compression 
after the air leaves the compressor cylinder. To reduce the 
amount of this loss, air compressors are designed with means 



88 TUNNELING 

to extract the heat from the air before it leaves the com- 
pressor cylinder. Air compressors may first be divided into 
two classes, according to the means employed for cooling the 
air, as follows: (1) Wet compressors, and (2) dry compress- 
ors. A wet compressor is one which introduces water directly 
into the cylinder during compression, and a dry compressor is 
one which admits no water to the air during compression. 
Wet compressors may be subdivided into two classes : (1) 
Those which inject water in the form of spray into the cylinder 
during compression, and (2) those which use a water piston 
for forcing the air into confinement. 

The following brief discussion of these various types of 
compressors is based on the concise practical discussion of 
Mr. W. L. Saunders, M. Am. Soc. C. E., in " Compressed Air 
Production." The highest isothermal results are obtained by 
the injection of water into the cylinders, since it is plain that 
the injection of cold water, in the shape of a finely divided 
spray, directly into the air during compression will lower the 
temperature to a greater degree than simply to surround the 
cylinder and parts by water jackets which is the means of cool- 
ing adopted with dry compressors. A serious obstacle to water 
injection, and that which condemns this type of compressor, is 
the influence of the injected water upon the air cylinder and 
parts. Even when pure water is used, the cylinders wear to 
such an extent as to produce leakage and to require reboring. 
The limitation to the speed of a compressor is also an important 
objection. The chief claim for the water piston compressor is 
that its piston is also its cooling device, and that the heat of 
compression is absorbed by the water. Water is so poor a 
conductor of heat, however, that without the addition of sprays 
it is safe to say that this compressor has scarcely any cooling 
advantages at all so far as the cooling of the air during com- 
pression is concerned. The water piston compressor operates 
at slow speed and is expensive. Its only advantage is that it 
has no dead spaces. In the dry compressor a sacrifice is made 



TUNNELS THROUGH HARD ROCK 89 

in the efficiency of the cooHng device to obtain low first cost, 
economy in space, light weight, higher speed, greater durability, 
and greater general availability. 

Air compressors are also distinguished as double acting and 
simple acting. They are simple acting when the cylinder is 
arranged to take in air at one stroke and force it out at the 
next, and they are double acting when they take in and force 
out air at each stroke. In form compressors may be simple or 
duplex. They are simple when they have but one cylinder, 
and duplex when they have two cylinders. A straight line or 
direct acting compressor is one in which the steam and air 
cylinders are set tandem. An indirect acting compressor is 
one in which the power is applied indirectly to the piston rod 
of the air cylinder through the medium of a crank. Mr. W. L. 
Saunders writes in regard to direct and indirect compression 
as follows : — 

" The experience of American manufacturers, which has been more exten- 
sive than that of others, has proved the value of direct compression as distin- 
guished from indirect. By direct compression is meant the application of 
power to resistance through a single straight rod. The steam and air cylinders 
are placed tandem. Such machines natui-ally show a low friction loss because 
of the direct application of power to resistance. This friction loss has been 
recorded as low as 5 %, while the best practice is about 10 % with the type which 
conveys the power through the angle of a crank shaft to a cylinder connected 
to the shaft through an additional rod." 

Receivers. — Compressed air is stored in receivers which are 
simply iron tanks capable of withstanding a high internal 
pressure. The purpose of these tanks is to provide a reservoir 
of compressed air, and also to allow the air to deposit its 
moisture. From the receivers the air is conveyed to the work- 
ings through iron pipes, which decrease gradually in diameter 
from the receivers to the front. 

Rock Drills. — The various forms of rock drills used in tun- 
neling have been described in Chapter III., and need not be 
considered in detail here except to say that American engi- 



90 TUNNELING 

neers usually employ percussion drills, while European 
engineers also use rotary drills extensively. A comparison 
between these two types of drills was made in excavating the 
Aarlberg tunnel in Austria, where the Brandt hydraulic 
rotary drill was used at one end, and the Ferroux percussion 
drill was used at the other end. The rock was a mica-schist. 
The average monthly progress was 412 ft., with a maximum 
of 64:6 ft., with the rotary drills, and an average of 454 ft. with 
the percussion drill. 

Excavation. — Since considerable time is required to get the 
power plant established, the excavation of rock tunnels is often 
begun by hand, but hand work is usually continued for no 
longer a period than is necessary to get the power plant in 
•operation. ' Generally speaking, the greatest difficulty is 
encountered in excavating the advanced drift or heading. 
Based on the mode of blasting employed, there are two methods 
of driving the advanced gallery, known as the circular cut 
and the center cut methods. In the first method a set of holes 
is first drilled near the center of the front in such a manner that 
they inclose a cone of rock ; the holes, starting at the perimeter 
of the base of the cone, converge toward a junction at its 
apex. Seldom more than four to six holes are comprised in 
this first set. Around these first holes are driven a ring 
of holes which inclose a cylinder of rock, and if necessary 
succeeding rings of holes are driven outside of the first ring. 
These holes are blasted in the order in which they are driven, 
the first set taking out a cone of rock, the second set enlarg- 
ing this cone to a cylinder, and the other sets enlarging this 
cylinder to the required dimensions of the heading. The number 
of holes, however, varies with the quality of rock and they are 
seldom driven deeper than 4 or 5 ft. This method of excavating 
the heading, which is commonly followed by European engineers, 
is illustrated in Figs. 50 to 52. In these figures are indicated 
the number of holes in each round and the sequence of rounds 
for the soft, medium and hard rock, as used in the Turchino 



TUNNELS THROUGH HARD ROCK 



91 



tunnel of the Geneva Ovada Asti line of the Mediterranean 
Railway of Italy. The heading was about 9 ft. square, and five 
sets of holes w^ere used in blasting, the depths being 3.91, 4.26 




In Sof+ RocK In Medium RocW \n Hard Rock 

Figs. 50 to 52. — Arrangement of Drill Holes in the Heading of Turchino Tunnel. 

and 4.6 ft. for soft, medium and hard rock, respectively, and the 
amount of dynamite consumed was 2.38, 3.91 and 5.1 pounds 
per cubic yard for the three classes of rock. 

In the center-cut method, 
which is the one commonly 
employed in America, the 
holes are arranged in vertical 
rows, and are driven from 
8 to 10 ft. deep. Fig. 53 
shows the arrangement of 
the holes, and the method 
of blasting them, as used in 
the excavation of the heading 
for the Fort George tunnel of 
the New York rapid transit. 
The two center rows of holes 
converge toward each other 
so as to take out a wedge 
of rock; others are bored 
straight, or parallel, with the 

vertical plane of the tunnel. Figs. 53 and 54. —Arrangement of Drill Holes 
rf^^ i i i j i • in the Heading of the Fort George Tunnel. 

Ihose bored around thepenm- 

eter are driven either outward or upward, according as they 

are located, close to the sides or roof of the tunnel. In this 




92 TUNNELING 

case, the holes of the center cut were driven 9 ft. deep, while 
all the other holes were bored to a depth of 8 ft. 

The width of the advanced gallery or heading depends upon 
the quality of the rock. In hard rock American engineers 
give it the full width of the tunnel section; but this cannot be 
done in loose or fissured rock, which has to be supported, the 
headings here being usually made about 8 X 8 ft. The wider 
heading is always preferable, where it is possible, since more 
room is available for removing the rock, and deeper holes can 
be bored and blasted. 

The important role played by the power plant and other 
mechanical installations in constructing tunnels through rock 
has already been mentioned. In some methods of soft-ground 
tunneling, and particularly in soft-ground subaqueous tunnel- 
ing, it is also often necessary to employ a mechanical installa- 
tion but slightly inferior in size and cost to those used in tunnel- 
ing rock. It is proposed to describe very briefly here a few 
typical individual plants of this character, which will in some 
respects give a better idea of this phase of tunnel work than the 
more general descriptions. 

Rock Tunnels. — The tunnels selected to illustrate the me- 
chanical installations employed in tunneling through rock are: 
The Mont Cenis, Hoosac Tunnel, the Cascade Tunnel, the Niagara 
Falls Power Tunnel, the Pahsades Tunnel, the Croton Aqueduct 
Tunnel, the Strickler Tunnel in America, and the Graveholz 
Tunnel and the Sonnstein Tunnel in Europe. In addition 
there will be found in another chapter of this book a description 
of the mechanical installations at the St. Gothard, Pennsylvania 
and other tunnels. 

Mont Cenis Power Plant. — The mechanical installation con- 
sisted of the Sommeilier air compressors built near the portals. 
The Sommeilier compressors, Mr. W. L. Saunders says, were 
operated as a ram, utilizing a natural head of water to force air 
at 80 lbs. pressure into a receiver. The column of water con- 
tained in the long pipe on the side of the hill was started and 



TUNNELS THROUGH HARD ROCK 93 

stopped automatically by valves controlled by engines. The 
weight and momentum of the water forced a volume of air with 
such a shock against the discharge valve that it was opened, 
and the air was discharged into the tank; the valve was then 
closed, the water checked; a portion of it was allowed to dis- 
charge, and the space was filled with air, which was in turn 
forced into the tank. Only 73 % of the power of the water was 
available, 27 % being lost by the friction of the water in the 
pipes, valves, bends, etc. Of the 73 % of net work, 49.4 was 
consumed in the perforators, and 23.6 in a dummy engine for 
working the valves of the compressors and for special venti- 
lation. 

The compressed air was conveyed from each end through a 
cast-iron pipe 7f in. in diameter, up to the front of the excava- 
tion. The joints of the pipes were made with turned faces, 
grooved to receive a ring of oakum which was tightly screwed 
and compressed into the joint. To ascertain the amount of 
leakage of the pipes, they and the tanks were filled with air 
compressed to 6 atmospheres, and the machines stopped; after 
12 hours the pressure was reduced to 5.7 atmospheres, or to 
95 % of the original pressure. 

Sommeiher's percussion drilling machines were used in the 
excavation of this tunnel. They were provided with 8 or 10 
drills acting at the same time, and mounted on carriages running 
on tracks. These were withdrawn to a safe place during the 
blasting, and advanced again after the broken rock was removed 
from the front and the new tracks laid. 

Machine shops were built at both ends of the tunnel for build- 
ing and repairing the drilHng machines, bits, tools, etc. A 
gas factory was built at each end for lighting purpose. 

Hoosac Tunnel. — The Hoosac tunnel on the Fitchburg R.R. 
in Massachusetts is 25,000 ft. long, and the longest tunnel in 
America. The material through which the tunnel was driven 
was chiefly hard granitic gneiss, conglomerate, and mica-schist 
rock. The excavation was conducted from the entrances and 



94 TUNNELING 

one shaft, the wide heading and single-bench method being 
employed, with the center-cut system of blasting which was 
here used for the first time. The tunnel was begun in 1854, 
and continued by hand until 1866, when the mechanical plant 
was installed. Most of the particular machines employed have 
now become obsolete, but as they were the first machines used 
for rock tunneling in America they deserve mention. The 
drills used were Burleigh percussion drills, operated by com- 
pressed air. Six of these drills were mounted on a single car- 
riage, and two carriages were used at each fronts The air to 
operate these drills was supphed by air compressors operated 
by water-power at the portals and steam-power at the shaft. 
The air compressors consisted of four horizontal single-acting 
air cyhnders with poppet valves and water injection. The 
compressors were designed by Mr. Thomas Deane, the chief 
engineer of the tunnel. 

Palisades Tunnel. — The Palisades tunnel was constructed to 
carry a double track railway line through the ridge of rocks 
bordering the west bank of the Hudson River and known as 
the Palisades. It was located about opposite 116th St. in New 
York City. The material penetrated was a hard trap rock very 
full of seams in places, which caused large fragments to fall 
from the roof. The excavation was made by a single wide 
heading and bench, employing the center-cut method of blast- 
ing with eight center holes and 16 side holes for the 7 X 18 ft. 
heading. Ingersoll-Sergeant 2J in. drills were used, four in 
each heading and six on each bench, and 30 ft. per 10 hours 
was considered good work for one drill. 

The power-plant was situated at the west portal of the tun- 
nel, and the power was transmitted by electricity and com- 
pressed air to the middle shaft and east portal workings. The 
plant consisted of eight 100 H. P. boilers, furnishing steam to 
four Rand duplex 18 X 22 in. air compressors, and an engine 
running a 30 arc light dynamo. The compressed air was carried 
over the ridge by pipes, varying from 10 ins. to 5 ins. in diam- 



TUNNELS THROUGH HARD ROCK 95 

eter, to the shaft and to the east portal, and was used for operat- 
ing the hoisting engines as well as the drills at these workings. 
Inside the tunnel, specially designed derrick cars were employed 
to handle large stones, they being also operated by compressed 
air. This car ran on a center track, while the mucking cars ran 
on side tracks, and it was employed to lift the bodies of the cars 
from the trucks, place them close to the front, being worked 
where large stone could be rolled into them, and return them 
to the trucks for removal. In addition to handling the car 
bodies the derrick was used to lift heavy stones. The haul- 
ing was done first by horse-power, and later by dummy 
locomotives. 

Croton Aqueduct Tunnel. — In the construction of the Croton 
Aqueduct for the water supply of New York City, a tunnel 31 
miles long was built, running from the Croton Dam to the Gate 
House at 135th St. in New^ York City. The section of the tun- 
nel varies in form, but is generally either a circular or a horse- 
shoe section. In all cases the section was designed to have a 
capacity for the flow of water equal to a cyHnder 14 ft. in diameter. 
To drive the tunnel, 40 shafts w^ere employed. The material 
penetrated was of almost every character, from quicksand 
to granitic rock, but the bulk of the work was in rock of some 
character. The excavation in rock was conducted by the wide 
heading and bench method, employing the center-cut method 
of blasting. Four air drills, mounted on two double-arm columns 
were employed in the heading. The drills for the bench work 
were mounted on tripods. Steam-power was used exclusively 
for operating the compressors, hoisting engines, ventilating 
fans and pumps; but the size and kind of boilers used, as well 
as the kind and capacity of the machines w^hich they operated, 
varied greatly, since a separate power-plant was employed for 
each shaft with a few exceptions. A description of the plant 
at one of the shafts will give an indication of the size and character 
of those at the other shafts, and for this purpose the plant at 
shaft 10 has been selected. 



96 TUNNELING 

At shaft 10 steam was provided by two Ingersoll boilers of 
80 H. P. each, and by a small upright boiler of 8 H. P. There 
were two 18 X 30 in. Ingersoll air compressors pumping into 
two 42 in. X 10 ft. and two 42 in. x 12 ft. Ingersoll receivers. 
In the excavation there were twelve 3J in. and six 3J in. Inger- 
soll drills, four drills mounted on two double arm columns 
being used on each heading, and the remainder mounted on 
tripods being used on the bench. Two Dickson cages operated 
by one 12 X 12 in. Dickson reversible double hoisting engine 
provided transportation for material and supplies up and down 
the shaft. A Thomson-Houston ten-light dynamo operated by 
a Lidgerwood engine provided light. Drainage was effected by 
means of two No. 9 and one No. 6 Cameron pumps. At this 
particular shaft the air exhausted from the drills gave ample 
ventilation, especially when after each blast the smoke was 
cleared away by a jet of compressed air. In other workings, 
however, where this means of ventilation was not sufficient, 
Baker blowers were generally employed. 

Strickler Tunnel. — The Strickler tunnel for the water supply 
of Colorado Springs, Col., is 6441 ft. long with a section of 
4 ft. X 7 ft. It penetrates the ridge connecting Pike's Peak 
and the Big Horn Mountains, at an elevation of 11,540 ft. above 
sea level. The material penetrated is a coarse porphyritic 
granite and morainal debris, the portion through the latter 
material being lined. The mechanical installation consisted 
of a water-power electric plant operating air compressors. 
The water from Buxton Creek having a fall of 2400 ft. was 
utilized to operate a 36 in. 220 H. P. Pelton water-wheel, which 
operated a 150 K. W. three-phase generator. From this gener- 
ator a 3500 volt current was transmitted to the east portal 
of the tunnel, where a step-down transformer reduced it to a 
220 volt current to the motor. The transmission line consisted 
of three No. 5 wires carried on cross-arm poles and provided 
with lightning arresters at intervals. The plant at the east 
portal of the tunnel consisted of a 75 H. P. electric motor, driving 



TUNNELS THROUGH HARD ROCK 97 

a 75 H. P. air compressor, and of small motors to drive a Sturte- 
vant blower for ventilation, to run the blacksmith shop, and 
to light the tunnel, shop, and yards. From the compressor 
air was piped into the tunnel at the east end, and also over the 
mountain to the west portal workings. Two drills were used at 
each end, and the air was also used for operating derricks and 
other machinery. For removing the spoil a trolley carrier 
system was employed. A longitudinal timber was fastened to 
the tunnel roof, directly in the apex of the roof arch. This 
timber carried by means of hangers a steel bar trolley rail on 
which the carriages ran. Outside of the portal this rail formed 
a loop, so that the carriage could pass around the loop and be 
taken back to the working face. Each carriage carried a steel 
span of 1} cu. ft. capacity, so suspended that by means of a 
tripping device it was automatically dumped when the proper 
point on the loop was reached. 

Niagara Falls Power Tunnel. — The tail-race tunnel built 
to carry away the water discharged from the turbines of the 
Niagara Falls Power Co., has a horse-shoe section 19 X 21 ft. 
and a length of 6700 ft. It was driven through rock from 
three shafts by the center-cut method of blasting. In sink- 
ing shaft No. very little water was encountered, but at shafts 
Nos. 1 and 2 an inflow of 800 gallons and 600 gallons per minute, 
respectively, was encountered. The principal plant was located 
at shaft No. 2, and consisted of eight 100 H.P. boilers, three 
18 X 30 in. Rand duplex air compressors, a Thomson-Houston 
electric-light plant, and a sawmill with a capacity of 20,000 ft. 
B. M. per day. The shafts were fitted with Otis automatic 
hoisting engines, with double cages at shafts Nos. 1 and 2, and 
a single cage at shaft No. 0. The drills used were 25 Rand 
drills and three Ingersoll-Sergeant drills. The pumping plant 
at shaft No. 2 consisted of four No. 7 and one No. 9 Cameron 
pumps, and that at shaft No. 2 consisted of two No. 7 and two 
No. 9 Cameron pumps and three Snow pumps. An auxihary 
boiler plant consisting of two 60 H. P. boilers was located at 



98 TUNNELING 

shaft No. 1, and another, consisting of one 75 H. P. boiler, was 
located at shaft No. 0. 

Cascade Tunnel. — The Cascade tunnel was built in 1886-88 
to carry the double tracks of the Northern Pacific Ry. through 
the Cascade Mountains in Washington. It is 9850 ft. long 
with a cross-section 16 J ft. wide and 22 ft. high, and is lined 
with masonry. The material penetrated was a basaltic rock, 
with a dip of the strata of about 5°. The rock was excavated 
by a wide heading and one bench, using the center-cut system 
of blasting. A strutting consisting of five-segment timber 
arches carried on side posts, spaced from 2 ft. to 4 ft. apart, 
and having a roof lagging of 4 X 6 in. timbers packed above 
with cord-wood. The mechanical plant of the tunnel is of 
particular interest, because of the fact that all the machinery 
and supplies had to be hauled from 82 to 87 miles by teams, 
over a road cut through the forests covering the mountain 
slopes. This work required from Feb.- 22 to July 15, 1886, to 
perform. In many places the grades were so steep that the 
wagons had to be hauled by block and tackle. The plant con- 
sisted of five engines, two water-wheels, five air compressors, 
eight 70 H. P. steam-boilers, four large exhaust fans, two com- 
plete electric arc-lighting plants, two fully equipped machine- 
shop outfits, 36 air drills, two locomotives, 60 dump cars, and 
two sawmill outfits, with the necessary accessories for these vari- 
ous machines. This plant was divided about equally between 
the two ends of the tunnel. The cost of the plant and of the 
work of getting it into position was S125,000. 

Graveholz Tunnel. — The Graveholz tunnel on the Bergen 
Railway in Norway is notable as being the longest tunnel in 
northern Europe, and also as being built for a single-track 
narrow-gauge railway. This tunnel is 17,400 feet long, and 
is located at an elevation of 2900 feet above sea-level. Only 
about 3 % of the length of the tunnel is lined. The mechani- 
cal installation consists of a turbine plant operating the various 
machines. There are two turbines of 100 H. P. and 120 H. P. 



TUNNELS THROUGH HARD ROCK 9& 

taking water from a reservoir on the mountain slope, and fur- 
nishing 220 H. P., which is distributed about as follows: Boring- 
machines, 60 H. P.; ventilation, 30 to 40 H. P.; electric loco- 
motives, 15 H. P.; machine shop, 15 H. P.; electric-lighting 
dynamo, 25 H. P. ; electric drills, the surplus, or some 40 H. P. 
The boring-machines and electric drills will be operated by the 
smaller 100 H. P. turbine. 

Sonnstein Tunnel. — The Sonnstein tunnel in Germany is 
particularly interesting because of the exclusive use of Brandt 
rotary drills. The tunnel was driven through dolomite and 
hard limestone by means of a drift and two side galleries. The 
dimensions of the drift were 7 J X 7 J ft. The power plant con- 
sisted of two steam pressure pumps, one accumulator, and four 
drills. The steam-boiler plant, in addition to operating the 
pumps, also supplied power for operating a rotary pump for 
drainage and a blower for ventilation. The hydraulic pressure 
required was 75 atmospheres in the dolomite, and from 85 to 
100 atmospheres in the limestone. The drift was excavated 
with five 3 J in. holes, one being placed at the center and driven 
parallel to the axis of the tunnel, and four being placed at the 
corners of a rectangle corresponding to the sides of the drift, 
and driven at an angle diverging from the center hole. The 
average depths of the holes were 4.3 ft., and the efficiency of 
the drills was 1 in. per minute. One drill was employed at 
each fronts and was operated by a machinist and two helpers, 
who worked eight-hour shifts, with a blast between shifts at 
first, and later twelve-hour shifts, with a blast between shifts. 
The 24 hours of the two shifts were divided as follows: boring 
the holes, 10.7 hours; charging the holes, 1.1 hours; removing 
the spoil, 11.7 hours; changing shifts, 0.5 hour. The average 
progress per day for each machine was 6.7 ft. The total cost 
of the plant was $17,450. 

St. Clair River Tunnel. — The submarine double-track rail- 
way tunnel under the St. Clair River for the Grand Trunk Ry. 
is 8500 ft. long, and was driven through clay by means of a 



100 TUNNELING 

shield, as described in the succeeding chapter on the shield 
system of tunneling. The mechanical plant installed for prose- 
cuting the work was very complete. To furnish steam to the 
air compressors, pumps, electric-hght engines, hoisting-engines, 
etc., a steam-plant was provided on each side of the river, con- 
sisting of three 70 H. P. and four 80 H. P. Scotch portable 
boilers. The air-compressor plant at each end consisted of 
two 20 X 24 in. Ingersoll air compressors. To furnish light to 
the workings, two 100 candle-power Edison dynamos were in- 
stalled on the American side, and two Ball dynamos of the same 
size were installed on the Canadian side. The dynamos on 
both sides were driven by Armington & Sims engines. These 
dynamos furnished light to the tunnel workings and to the 
machine-shops and power-plant at each end. Root blowers of 
10,000 cu. ft. per minute capacity provided ventilation. The 
pumping plant consisted of one set of pumps installed for per- 
manent drainage, and another set installed for drainage during 
construction, and also to remain in place as a part of the per- 
manent plant. The latter set consisted of two 500 gallon Worth- 
ington duplex pumps set first outside of each air lock, closing 
the ends of the river portion of the tunnel. For permanent 
drainage, a drainage shaft was sunk on the Canadian side of the 
river, and connected with a pump at the bottom of the open-cut 
approach. In this shaft were placed a vertical, direct-acting, 
compound-condensing pumping engine with two lOJ in. high- 
pressure and two 33| in. low-pressure cylinders of 24 in. stroke, 
connected to double-acting pumps with a capacity of 3000 
gallons per minute, and also two duplex pumps of 500 gallons 
capacity per minute. For permanent drainage on the American 
side, four Worthington pumps of 3000 gallons' capacity were 
installed in a pump-house set back into the slope of the open- 
cut approach. For the permai^^nt drainage of the tunnel 
proper two 400 gallon pumps were placed at the lowest point 
of the tunnel grade. Spoil coming from the tunnel proper was 
hoisted to the top of the open cut by derricks operated by two 



TUNNELS THROUGH HARD ROCK 101 

50 H. P. Lidgerwood hoisting-engines. The pressure pumping 
plant for supplying water to the hydraulic shield-jacks at each 
end of the tunnel consisted of duplex direct-acting engines 
with 12 in. steam cylinders and 1 in. water cylinders, supply- 
ing water at a pressure of 2000 lbs. per sq. in. 



102 



TUNNELING 



CHAPTER X. 
TUNNELS THROUGH HARD ROCK (Continued). 



EXCAVATION BY DRIFTS: THE SIMPLON AND MURRAY HILL 

TUNNELS. 

General Description. — The method of tunneling through hard 
rock by drifts is preferred by European engineers. All the great 
Alpine tunnels, from the Mont Cenis tunnel to the Simplon, 
are examples of tunnehng by drifts. In this method the se- 
quence of excavation is shown diagrammatically by Fig. 55. 

The work begins by excavating a 
drift close to the floor of the pro- 
posed tunnel (as shown in the center 
of the figure) and far in advance of 
the excavation of any other part. 
The section marked 2 is next re- 
moved and still later the portions 
marked 3. Then with the removal 
of the parts marked 4 the whole 
section of the tunnel will be open. 

The drift is usually strutted by 
means of side posts carrying a cap- 
piece placed at intervals, and hav- 
ing a ceiling of longitudinal planks resting on the successive caps. 
In hard rock the roof of the section does not, as a rule, require 
regular strutting, occasional supports being placed at intervals 
to prevent the fall of isolated fragments: When the rock is dis- 
integrated or full of seams, a regular strutting may be necessary, 
and this may be either longitudinal or polygonal in type. When 
longitudinal strutting is employed, a sill is laid across the roof of 



/ ^ 


2 


3 \ 


b 




i 


\ 

\ 




1 
1 


\ 




1 


\ 4 


1 


4/ 


\ 




/ 


\ 




; 
/ 


\ 




/ 


\ 
i , 




/ 

/ 

1 L 1 



Fig. 55. — Diagram Showing Se- 
quence of Excavations in Drift 
Method of Tunneling Rock. 



TUNNELS THROUGH HARD ROCK 103 

the drift, and upon this are set up two struts converging toward 
the top and supporting a cap-piece close to the roof. On this 
cap-piece are placed the first longitudinal crown bars carrying 
transverse poling-boards. Additional props standing on the sill 
and radiating outward are inserted as parts No. 3 are excavated. 
These radial props carry longitudinal bars which in turn support 
transverse poling-boards. When polygonal strutting is used, 
it may take the form of three or five segment arches of heavy 
timbers. 

In hard rock tunnels, as a rule, there is no danger of caving in 
because of heavy pressures, and the whole section is left open 
for some time before it is lined. The lining may be of concrete 
masonry, but in many long tunnels, excavated through hard 
rock, the side walls are lined with rubble masonry and the arch 
with brick, and, in some instances, even the arch has been hned 
with rubble masonry. With skilful laborers at hand the rubble 
masonry lining has proved most efficient and economical, be- 
cause the rock is utilized as it is excavated without any further 
operation. Concrete, however, is more extensively employed 
for lining tunnels than any other material. 

Tunnels excavated by drifts enable simple means of hauling 
to be employed, and this is one of the reasons why the method 
finds so much favor with European engineers. The tracks 
are laid along the floor of the drift, and carry all the spoil from 
parts Nos. 2, 3, and 4, as well as from the front of the drift 
itself. As fast as the full section is completed, this single track 
in the drift is replaced by two tracks running close to the sides 
of the tunnel, or by a broad-gauge track with a third rail. 

THE SIMPLON TUNNEL.* 

Before entering upon a description of the constructive de- 
tails of this, the longest railway tunnel in the world, it may be 
well to give a general idea of the undertaking. Many schemes 

* Abstract from a paper read before the Institution of Civil Engineers by 
Charles B. Fox, Jan. 26, 1900. 



104 TUNNELING 

for the connection of Italy and Switzerland by a railway near 
the Simplon Road Pass have been devised, including one in- 
volving no great length of underground work, the line mounting 
by steep gradients and sharp curves. The present scheme, 
put forward in 1881 by the Jura-Simplon Ry. Co., consists 
broadly of piercing the Alps between Brigue, the present rail- 
way terminus in the Rhone Valley, and Iselle, in the gorge of 
the Diveria, on the Italian side, from which village the railway 
will descend to the existing southern terminus at Domo d'Ossola, 
a distance of about 11 miles. 

In conjunction with this scheme a second tunnel is pro- 
posed, to pierce the Bernese Alps under the Lotschen Pass 
from Mittholz to a point near Turtman in the Rhone Valley; 
and thus, instead of the long detour by Lausanne and the Lake 
of Geneva, there will be an almost direct line from Berne to 
Milan via Thun, Brigue, and Domo d'Ossola. 

Starting from Brigue, the new line, running gently up the 
valley for IJ miles, will, on account of the proximity of the 
Rhone, which has already been slightly diverted, enter the 
tunnels on a curve to the right of 1050 ft. radius. At a dis- 
tance of 153 yards from the entrance, the straight portion 
of the tunnel commences, and extends for 12 miles. The line 
then curves to the left with a radius of 1311 ft. before emerging 
on the left bank of the Diveria. Commencing at the northern 
entrance, a gradient of 1 in 500 (the minimum for efficient 
drainage) rises for a length of 5^ miles to a level length of 550 
yards in the center, and then a gradient of 1 in 143 descends 
to the Itahan side. On the way to Domo d'Ossola one helical 
tunnel will be necessary, as has been carried out on the St. 
Gothard. There will be eventually two parallel tunnels having 
their centers 56 ft. apart, each carrying one fine of way; but 
at the present time only one heading, that known as No. 1, 
is being excavated to full size. No. 2 being left, masonry lined 
where necessary, for future developments. By means of cross 
headings every 220 yds. the problems of transport and ventila- 



TUNNELS THROUGH HARD ROCK 105 

tion are greatly facilitated, as will be seen- later. As both 
entrances are on curves, a small " gallery of direction " is neces- 
sary, to allow corrections of alinement to be made direct from 
the two observatories on the axis of the tunnel. 

The outside installations are as nearly in duplicate as cir- 
cumstances will allow, and consist of the necessary offices, 
workshops, engine-sheds, power-houses, smithies, and the nu- 
merous buildings entailed by an important engineering scheme. 
Great care is taken that the miners and men working in the 
tunnel shall not suffer from the sudden change from the warm 
headings to the cold Alpine air outside; and for this purpose 
a large building is in course of erection, where they will be 
able to take off their damp working clothes, have a hot and 
cold douche, put on a warm dry suit, and obtain refreshments 
at a moderate cost before returning to their homes. Instead 
of each man having a locker in which to stow his clothes, a 
perfect forest of cords hangs down from the wooden ceiling, 
25 ft. above floor-level, each cord passing over its own pulleys 
and down the wall to a numbered belaying-pin. Each cord 
supports three hooks and a soap-dish, which, when loaded with 
their owner's property, are hauled up to the ceiling out of the 
way. There are 2000 of these cords, spaced 1 ft. 6 ins. apart, 
one to each man. The engineers and foremen are more privi- 
leged, being provided with dressing-rooms and baths, partitioned 
off from the two main halls. An extensive clothes washing 
and drying plant has been laid down, and also a large restau- 
rant and canteen. At Iselle, a magazine holding 2200 lbs. of 
dynamite is surrounded and divided into two separate parts by 
earth-banks, 16 ft. high. The two wooden houses, in which 
the explosive is stored, are warmed by hot-water pipes to a 
temperature between 61° F. and 77° F., and are watched by 
a military patrol; but at Brigue a dynamite manufactory, 
started by an enterprising company at the time of the com- 
mencement of the works, suppHes this commodity at frequent 
intervals, thereby avoiding the necessity of storing in such 



106 TUNNELING 

large quantities. This dynamite factory has been largely in- 
creased, and supplies dynamite to nearly all the mining and 
tunneling enterprises in Switzerland. 

Geological Conditions. — Before the Simplon tunnel was au- 
thorized, expert evidence was taken as to the feasibility of 
the project. The forecasts of the three engineers chosen, in 
reference to the rock to be encountered and its probable tem- 
perature, have, as far as the galleries have gone ( an aggregate 
distance of nearly 2 J miles), generally been found correct. 
At the north end, a dark argillaceous schist veined with quartz 
was met with, and from time to time beds of gypsum and dolomite 
have been traversed, the dip of the strata being on the whole 
favorable to progress, though timbering is resorted to at danger- 
ous places. Water was plentiful at the- commencement ; in fact, 
one inrush has not been stopped, and is still flowing down the 
heading. The total quantity of water flowing from the tunnel 
mouth is 16 gallons per second, of which 2 gallons per second 
are accounted for by the drilling machines. At Iselle, how- 
ever, a very hard antigorio gneiss obtains, and is likely to 
extend for 4 miles. Very dry and very compact, it requires 
no timbering, and represents no great difflculty to the powerful 
Brandt rock-drills, which work under a head of 3280 ft. of 
water. 

The temperature of the rock depends not only on the depth 
from the surface, but largely upon the general form of that sur- 
face combined with the conductivity of the rock. Taking 
these points into consideration with the experience gained from 
the construction of the St. Gothard tunnel, 95° F. was esti- 
mated as the probable maximum temperature, owing to the 
height of Monte Leone (11,660 ft.), which lies almost directly 
over the tunnel axis. 

Survey. — After having determined upon the general position 
of the tunnels, taking into consideration the necessary gradi- 
ents, the temperature of the rock, and a large bed of trouble- 
some gypsum on the north side, two fixed points on the pro- 



TUNNELS THROUGH HARD ROCK 107 

posed center line were taken, one at each entrance of tunnel 
No. 1, and the bearings of these two points, with reference to 
a triangulation survey made in 1876, were calculated sufficiently 
accurately to determine, for the time being, the direction of 
the tunnel. In 1898, a new triangulation survey was made, 
taking in eleven summits, Monte Leone holding the central 
position. This survey was tied into that of the Wasenhorn 
and Faulhorn, made by the Swiss Government, and the accuracy 
was such that the probable error in the meeting of the two 
headings is only 6 cms. or 2^ ins. 

On the top of each summit is placed a signal, consisting of 
a small pillar of masonry founded on rock, and capped with a 
sharp pointed cone of zinc, 1 ft. 6 ins. high. An observatory 
was built at each end of the tunnel in such a position that three 
of the summits could be seen, a condition very difficult to fulfill 
on the south side owing to the depth of the gorge, the moun- 
tains on either side being over 7000 ft. high. Having taken 
the angles to and from each visible signal, and therefrom having 
calculated the direction of the tunnel, it was necessary to fix, 
with extreme accuracy, sighting-points on the axis of the tunnel, 
in order to avoid sighting on to the surrounding peaks for each 
subsequent correction of the alinement of the galleries. To 
do this, a theodolite 24 ins. long and 2f ins. in diameter, with 
a magnifying pow^r of 40 times, was set up in the observatory, 
and about 100 readings were taken of the angles between the 
surrounding signals and the required sighting-points. In this 
manner the error fikely to occur was diminished to less than 1^ 
Thus at the north end two points were found about 550 yds. 
before and behind the observatory, while on the south side, 
owing to the narrowness of the gorge, the points could only be 
placed at 82 yds. and 126 yds. in front. One of these sighting- 
points consists of a fine scratch ruled on a piece of glass fixed 
in an iron frame, behind which is placed an acetylene lamp, — - 
corrections of alinement are always done by night, — the whole 
being rigidly fixed into a niche cut in the rock and pro- 



108 TUNNELING 

tected from climatic and other disturbing agencies by an iron 
plate. 

Method of Checking Alinement. — The direction of heading 
No. 1 is checked by experts from the Government Survey De- 
partment at Lausanne about three times a year, and for this 
purpose a transit instrument is set up in the observatory. A 
number of three-legged iron tables are placed at intervals of 
1 mile or 2 miles along the axis of tunnel No. 1, and upon each 
of these is placed a horizontal plane, movable by means of 
an adjusting screw, in a direction at right angles to the axis, 
along a graduated scale. On this plane are small sockets, into 
which the legs of an acetylene lamp and screen, or of the transit 
instrument, can be quickly and accurately placed. The screen 
has a vertical slit, 3 ins. in height, and, variable between i| in. 
and T^6 in.. in breadth, according to the state of the atmosphere, 
and at a distance shows a fine thread of light. The instrument, 
having first been sighted on to the illuminated scratch of the 
sighting-point, is directed up the tunnel, where a thread of 
light is shown from the first table. With the aid of a telephone 
this light is adjusted so that its image is exactly coincident 
with the cross hairs, and the reading on the graduated scale is 
noted. This is done four or five times, the average of these 
readings being taken as correct, and the plane is clamped to 
that average. The instrument is then taken to the first table 
and is placed quickly and accurately over the point just found 
(by means of the sockets), and the lamp is carried to the observa- 
tory. After first sighting back, a second point is given on the 
second table, and so on. These points are marked either tem- 
porarily in the roof of the heading by a short piece of cord hanging 
down, or permanently by a brass point held by a small steel 
cylinder, 8 ins. long and 3 ins. in diameter, embedded in concrete 
in the rock floor, and protected by a circular casting, also sunk 
in cement concrete, holding an iron cover resembling that of 
a small manhole. From time to time the alinement is checked 
from these points by the engineers, and after each blast the 



TUNNELS THROUGH HARD ROCK 10& 

general direction is given by the hand from the temporary 
points. To check the results of the triangulation survey, astro- 
nomical observations have been taken simultaneously at each 
end. With regard to the levels, those given on the excellent 
Government surveys have been taken as correct, but they have 
also been checked over the pass. 

Details of Tunnels. — In cross-section, tunnel No. 1 is 13 ft. 
7 ins. wide at formation level, increasing to 16 ft. 5 ins., with 
a total height of 18 ft. above rail-level, and a cross-sectional 
area of about 250 sq. ft. This large section will allow of small 
repairs being executed in the roof without interruption of the 
traffic, and will also allow of strengthening the walls by addi- 
tional masonry on the inside. The thickness of the lining, 
never wholly absent, and the material of which it is composed, 
depend upon the pressure to be resisted, and only in the worst 
case is an invert resorted to. The side drain, to which the rock 
floor is made to slope, will be composed of half-pipes of 
7 to 1 cement concrete. The roof is constructed of radial 
stones. 

Tunnel No. 2, being left as a heading, is driven on that side 
nearest to No. 1, to minimize the length of the cross-headings, 
and measures 10 ft. 2 ins. wide by 6 ft. 7 ins. high. Masonry 
is used only where necessary, and in that case is so built as to 
form part of the lining of the tunnel when eventually com- 
pleted. Concrete is put in to form a foundation for the side 
wall, and a w^ater channel. The cross-headings, connecting the 
two parallel headings, occur every 220 yds., and are placed at 
an angle of 56° to the axis of the tunnel, to avoid sharp curves 
in the contractors' railway Hues. They will eventually be used 
as much as possible for refuges, chambers for storing the tools 
and equipment of the platelayers, and signal-cabins. The ref- 
uges, 6 ft. 7 ins. wide by 6 ft. 7 ins. high and 3 ft. 3 ins. deep, 
occur every 110 yards, every tenth being enlarged to 9 ft. 10 
ins. wide by 9 ft. 10 ins. deep and 10 ft. 2 ins. high, still larger 
chambers being constructed at greater intervals. 



110 TUNNELING 

Method of Excavation. — The work at each end of the tunnel 
is carried on quite independently, consequently, though similar 
in principle, the methods vary in detail, apart from the fact that 
different geological strata require different treatment. Broadly 
speaking, the two parallel headings, each 59 sq. ft. in section, 
are first driven by means of drilHng-machines and the use of 
dynamite, this work being carried on day and night, seven days 
in the week; No. 1 heading is then enlarged to full size by hand- 
drilling and dynamite. On the Itahan side, where the rock 
is hard and compact, breakups are made at intervals of 50 yds., 
and a top gallery is driven in both directions, but, for venti- 
lation reasons, is never allowed to get more than 4 yds. ahead 
of the break-up, which is gradually lengthened and widened 
to the required section. No timbering is required, except to 
facilitate the excavation and the construction of the side walls. 
Steel centers are employed for the arch; they entail fewer sup- 
ports, give more room, and are capable of being used over again 
more frequently without damage. They consist of two I-beams 
bent to a template and riveted together at the crown, resting 
at either side on scaffolding at intervals of 6 ft. ; longitudinals 
12 ft. by 4 ins. by 4 ins. support the roof. Hand rock-drilHng 
is carried out in the ordinary way, one man holding the tool and 
a second striking; measurements of excavation are taken every 
2 or 3 yds., a plumb-line is suspended from the center of the 
roof, and at every half-meter (20 ins.) of height horizontal 
measurements are taken to each side. 

At the Brigue end a softer rock is encountered, necessitat- 
ing at times heavy timbering in the heading, and especially in 
the final excavation to full size, Fig. 56. The bottom heading, 
6 ft. 6 in. high, is driven in the center, and the heading is then 
widened to the full extent and timbered; the concrete forming 
the water channel and the foundation for one side wall is put 
in; the side walls are built to a height of 6 ft. 6 ins., and the tunnel 
is fully excavated to a further height of 6 ft. 6 ins. from the 
first staging. The side walls are then continued up for the 



TUNNELS THROUGH HARD ROCK 



111 



second 6 ft. 6 ins., and 
from the second floor 
a third height of 6 ft. 
6 ins. is excavated and 
timbered. Finally the 
crown is cleared out, 
heavy wooden centers 
are put in, the arch is 
turned and all tim- 
bers are withdrawn 
except the top pohng- 
boards, supporting 
the loose rock. 

The masonry for 
the side walls is ob- 
tained either from the 
tunnel itself or from 
a neighboring quarry, 
and varies in charac- 
ter according to the 
pressure ; but the face 
of the arch is always 
of cut or artificial 
stones, the latter be- 
ing 7 to 1 cement 
concrete. Where the 
alinement heading, or 
the " gallery of direc- 
tion," joins the curv- 
ing portion of tunnel 
No. 1, the section is 
very much greater, and necessitates special timbering. 

Transport (Italian Side). — A small line of railway, 2 ft. 7J 
ins. gauge, with 40-lb. rails, enters all three portals; but since 
the con-struction of a wooden bridge over the Diveria, the route 




Fig. 56. — Sketches Showing Sequence of Work in 
Excavating and Lining the Simplon Tunnel. ' 



112 TUNNELING 

through the '' gallery of direction/' across heading No. 2, to 
tunnel No. 1, is used exclusively; this railway leads to the face 
in both headings, and, where convenient, from one heading to 
the other by the cross-galleries. Different types of wagons are 
in use; but in general they are four-wheeled, non-tipping box 
wagons, supplied with brakes and holding 2 cu. yds. of debris. 
A special type of locomotive is used, designed to pass round 
curves of 50 ft. radius, and supplied with a specially large boiler 
to avoid firing in the tunnel. 

Method of Working. — The drilling-machines employed are of 
the' Brandt type. Fig. 57, and are mounted in the following 
manner: A small four-wheeled carriage supports at its center 




Fig. 57. — General Details of the Brandt Rotary Drills Employed at the Simplon Tunnel. 

a beam, the shorter arm of which carries the boring mechanism 
and the longer a counterpoise ; near its center is the distributor. 
In the short arm is a clamp holding the rack-bar or butting 
column, which is a wrought-iron cylinder with a plunger con- 
stituting a ram, and is jammed by hydraulic pressure betweea 
the walls of the heading, thus forming a rigid support for the 
boring-machine, and an efficient abutment against the reaction 
of the drill. This rack-bar can be rotated on its clamp in a» 



TUNNELS THROUGH HAKD ROCK 113 

plane parallel to the axis of the beam. Three or four separate 
boring-machines can be mounted on the rack-bar, and can be 
adjusted in any reasonable position. 

The boring-machine performs the double function of con- 
tinually pressing the drill into the rock by means of a hollow 
ram (1) and of imparting to the drill and ram a uniform rotary 
motion. This rotary motion is given by a twin cyHnder single- 
acting hydraulic motor (E), the two pistons, of 2| ins. stroke, 
acting reciprocally as valves. The cranks are fixed at an angle 
of 90° to each other on the shaft, which carries a worm, gearing 
with a worm-wheel (Q) mounted upon the shell (R) of the 
hollow ram (1), and this shell in turn engages the ram by a 
long feather, leaving it free to slide axially to or from the face 
of the rock. The average speed of the motor is 150 revolutions 
to 200 revolutions per minute, the maximum speed being 300 
revolutions per minute. The loss of power between the worm 
and worm-wheel is only 15 % at the most; the worm being of 
hardened steel and the wheel of gun-metal, the two surfaces in 
contact acquire a high degree of pohsh, resulting in little wear- 
ing or heating. Taking into consideration all other sources of 
loss, 70 % of the total power is utilized. The pressure on the 
drill is exerted by a cyhnder and hollow ram (/), which revolves 
about the differential piston {S), which is fixed to the envelope 
holding the shell (R). This envelope is rigidly connected to 
the bed-plate of the motor, and, by means of the vertical hinge 
and pin (T), is held by the clamp (F) embracing the rack-bar. 
\Vhen water is admitted to the space in front of the differential 
piston the ram carrying the drilling-tool is thrust forward, and 
when admitted to the annular space behind the piston, the ram 
recedes, withdrawing the tool from the blast-hole. The drill 
proper is a hollow tube of tough steel 2| ins. in external diame- 
ter, armed with three or four sharp and hardened teeth, and 
makes from five to ten revolutions per minute, according to the 
nature of the rock. When the ram has reached the end of its 
stroke of 2 ft. 2 J ins., the tool is quickly withdrawn from the 



114 TUNNELING 

hole and unscrewed from the ram; an extension rod is then 
screwed into the tool and into the ram, and the boring is con- 
tinued, additional lengths being added as the tool grinds for- 
ward; each change of tool or rod takes about 15 sees, to 25 
sees, to perform. The extension rods are forged steel tubes, 
fitted with four-threaded screws, and having the same external 
diameter as the drill. They are made in standard lengths of 

2 ft. 8 ins., 1 ft. 10 ins., and 11| ins. The total weight of the 
drilling-machine is 264 lbs., and that of the rack-bar when full 
of water is 308 lbs. The exhaust water from the two motor 
cylinders escapes through a tube in the center of the ram and 
along the bore of the extension rods and drill, thereby scouring 
away the debris and keeping the drill cool; any superfluous 
w^ater finds an exit through a hose below the motors and thence 
away down the heading. The distributor, already mentioned, 
supplies each boring-machine and the rack-bar with hydraulic 
pressure from the mains, with which connection is effected by 
means of flexible or articulated pipe connections, allowing free- 
dom in all directions. The area of the piston for advancing 
the tool is 15 J sq. ins., which, under a pressure of 1470 lbs. per 
sq. in., gives a pressure of over 10 tons on the tool, while for 
withdrawing the tool 2 J tons is available. In the rock found at 
Iselle, namely, antigorio gneiss, a hole 2| ins. in diameter and 

3 ft. 3 ins. in length is drilled, normally, in 12 mins. to 25 mins.; 
a daily rate of advance of 18 ft. to 19 ft. 6 ins. is made in a head- 
ing having a minimum cross-section of 59 sq. ft.; the time taken 
to drill ten to twelve holes, 4 ft. 7 ins. deep, is 2J hrs. 

When the debris resulting from one operation has been suffi- 
ciently cleared away, a steel flooring, which is provided near 
the face to enable shoveling to be more easily done, and to 
give an even floor for the wheels of the drilHng-carriage, is 
laid bare at the head of the line of rails, and the drilling-machines 
are brought up on their carriage by eight or ten men. When 
advanced sufficiently close to the face, the rack-bar is slewed 
round across the gallery and is wedged up against the rock 



TUNNELS THROUGH HARD ROCK 115 

sides; connection is made between the distributor and the 
hydrauHc main, by means of the flexible pipe, and pressure 
is suppHed by a small copper tube to the rack-bar ram, thereby 
rigidly holding the machine. Next, connections are made be- 
tween the three drilling-machines and the distributor, and in 
20 mins. from the time the machine was brought up all three 
drills are hard at work, water pouring from the holes. 

The noise of the motors and grinding-tools is sufficient to 
drown all but shouts; and where the extension rods do not fit 
tightly, small jets of water play in all directions, necessitating 
the wearing of tarpaulins by the men directing the tools. Light- 
ing is done wholly by small oil-lamps, provided with a hook 
to facilitate fixing in any crack in the rock; electricity will 
probably be used to fight that portion of the tunnel which is 
completed. 

Two men are alloted to each drill, one to drive the motor, 
the other to direct and replenish the tool, one foreman and two' 
men in reserve completing the gang. A small hammer is freely 
used to loosen the screw joints of the extension rods and drill. 
A hole is usuafiy commenced by a two-edged flat-pointed tool, 
until a sufficient depth is reached to prevent the circular tool 
from wandering over the face of the rock, but in many instances 
the hole is commenced with a circular tool. The exhaust 
water during this period flows away by the hose underneath 
the motor. In the antigorio gneiss, ten to twelve holes are 
drilled for each attack, three to four in the center to a depth of 
3 ft. 3 ins., the remainder, disposed round the outside of the 
face, having a depth of 4 ft. 7 ins. The average time taken to 
complete the holes is If hr. to 2 J hrs. Instead of pulverizing 
the rock, as do the diamond drills, it is found that the rock is 
crushed, and that headway is gained somewhat in the manner 
of a circular saw through wood. The core of rock inside the 
tool breaks up into smafi pieces, and can be taken out if necessary 
when the drill requires lengthening. 

The lowest holes, incHned downwards, are full of water; 



116 ^ TUNNELING 

consequently two detonators and two fuses are inserted, but 
apart from this, water has little effect on the charge. The 
fuses of the central holes are brought together and cut off shorter 
than those of the outer holes, in order that they may explode 
first to increase the effect of the outer charges. All portable 
objects, such as drills, pipe connections, tools, etc., have mean- 
while been carried back; the steel flooring is covered over with 
a layer of debris to prevent injury from falling rock, and to 
the end of the hydraulic main is screwed a brass plug pierced 
by five holes; and immediately the explosions occur a valve is 
opened in the tunnel, and five jets of water play upon the rock, 
laying the dust and clearing the air. The necessity for this 
was shown on one occasion when this nozzle was broken by the 
explosion and the water had to be turned off immediately to 
avoid useless waste; on reaching the face, the atmosphere was 
found to be so highly charged with dust and smoke that it was 
impossible to distinguish the stones at the feet, although a lamp 
had been placed on the ground; and despite the fact that the 
air tube was in full blast, the men experienced great difficulty 
in breathing. A truck is now brought up, and four men clear 
a passage in front, through the heap of debris, two with picks 
and two with shovels, while on either side and behind are as many 
men as space will permit. The stone is thrown either to the sides 
of the heading or into the wagon, shoveling being greatly aided 
by the steel flooring, which, before the explosion, had been laid 
over the rails for nearly 10 yds. down the tunnel to receive the 
falHng rock. These steel plates are taken up when cleared, and 
the wagon is pushed forward until the drilling-machine can be 
brought up again, leaving the remaining debris at the sides to be 
handled at leisure during the next attack. The roof and side 
walls are, of course, carefully examined with the pick, to discover 
and detach any loose or hanging rock. The times taken for each 
portion of the attack in this particular antigorio gneiss are as 
follows: Bringing up and adjustment of drills, 20 mins.; drill- 
ing, between If hr. and 2 J hrs.; charging and firing, 15 mins.; 



TUNNELS THROUGH HARD ROCK 117 

clearing away debris, 2 hrs.; or for one whole a,ttack, between 
4i hrs. and 5 J hrs., resulting in an advance of 3 ft. 9 in., or a 
daily advance of nearly 18 ft. 

From this it appears that the time spent in clearing away 
the debris equals that taken up in drilling, and it in this clear- 
ing that a saving of time is likely to be effected rather than in 
the process of drilling. Many schemes have been tried, such as 
a mechanical plow for making a passage; at Brigue, " marin- 
age," or clearing by means of powerful high-pressure water-jets, 
directed down the tunnel, was tried, but the idea is not yet 
sufficiently developed. 

Another series of experiments has been tried at Brigue with 
regard to the utilization of liquid air as an explosive agent 
instead of dynamite; and for this purpose a plant has been 
laid down, consisting of one ammonia-compressor, two air-com- 
pressors, and two refrigerators, furnishing j\ gallon of liquid 
air per hour at an expenditure of 17 H. P. The system used is 
that of Professor Linde, who himself directs the experiments. 
The great difficulty experienced is that of shortening the interval 
of time that must elapse between the manufacture of the cart- 
ridge and its explosion. The liquid oxygen, with which the 
cartridge, containing kieselguhr (silicious earth) and paraffin, is 
saturated, evaporates very readily, losing power every moment; 
hence the effect of each cartridge cannot be guaranteed, and 
though it is an exceedingly powerful explosive when used im- 
mediately after manufacture, no practical result has yet been 
obtained. 

Power Station. — Water is abundant at either end, and there- 
fore hydraulic power is the motive force employed. On the 
Italian side, a dam 5 ft. high has been thrown across the Diveria 
at a point near the Swiss frontier, about 3 miles above the site 
of the installations. A portion of the water thus held back 
enters, through regulating doors and gratings, a masonry channel 
leading to two parallel settling tanks, each 111 ft. by 16 ft., 
whence, after dropping all its sand and solid matter, the now 



118 TUNNELING 

pure water passes into the water-house, and, after flowing over 
a dam, through a grating and past the admission doors, enters 
a metallic conduit of 3-ft. pipes. Each of the settling tanks 
and the approach canal are provided with doors at the lower 
end leading direct to the river, through which all the sand and 
solid matter deposited can be scoured naturally by allowing 
the river- water to rush freely through. For this purpose the 
floor of the basins is on an average gradient of 1 in 30. For 
a similar reason the river-bed just outside the entrance to the 
approach canal is lined with wooden planks, from which the 
stones collecting behind the dam can be scoured by allowing 
an iron flap, hinged at the bottom, to change its position from 
the vertical to the horizontal in a gap left purposely in the 
dam, so causing a rushing torrent to sweep it clean. 
The chief levels are : 

Level of water at dam 794 . 00 meters above sea level. 

" in water-house 793.70 " " " " 

" at turbines 618.50 " " " " 

giving a total fall of 175.20 ms. or 570 ft., and a pressure of 
17.52 atmospheres. 

The quantity of water capable of being taken from the Diveria 
in winter, when the rivers which are dependent upon the moun- 
tain snows for their supply are at their lowest, is calculated 
to be 352 gallons per second. Thus, taking the fall to be 
diminished by friction, etc., to 440 ft., and the useful effect at 
70 %, there is obtained 2000 H. P. on the turbine shaft. 

The metallic conduit varies in material according to the 
pressure; thus cast-iron pipes 3 ft. in diameter and |f in. thick 
are used up to a pressure of 2 atmospheres, from which point 
they are of wrought-iron. The cast-iron portion has of late 
caused a good deal of trouble, owing to settlement of the piers 
causing occasional bursts, consequently a masonry pier has 
been placed under each joint of this portion. The following 
table gives the thicknesses and diameters, varjdng with the 
pressure : 



TUNNELS THEOUGH HARD ROCK 



119 



Water 
Pressure. 


Thickness. 


Diameter. 


, Weight per 
Yard. 


Head in Feet. 


Milli- 
meters. 


Inch. 


Feet. 


Inches. 


Lbs. 


246 

311 
360 
393 
426 
476 
590 


6 

7 

8 

9 

10 

12 

16 


1 


3 
3 
3 
3 
3 
3 
3 








31 


326 
383 
431 
483 
556 
651 
977 



This pipe is supported every 30 ft. on small masonry piers, 
on the top of which is placed a block of wood hollowed out to 
receive the pipe, thus allowing any movement due to the con- 
traction and expansion of the conduit. However, to prevent 
this movement becoming excessive, the pipe is passed at intervals 
of 300 yds. to 500 yds. through a cubical block of masonry of 
13 ft. side, strengthened by longitudinal tie-bars. Five bands 
of angle-bar riveted round the pipe, with their flanges embedded 
in the masonry, constitute a rigid fixed point. Straw mats are 
thrown over the pipe where it is exposed to the sun. The tem- 
perature of the conduit is not, however, found to vary greatly, 
since the pipe is kept full of water. To supply the rock-drills 
with water at a maximum pressure of 100 atmospheres, or 
1470 lbs. per sq. in., a plant of four pairs of high-pressure pumps 
has been laid down, and a still larger addition is in course of 
erection. At present, two Pelton turbines of 250 H.P. each, 
running at 170 revolutions per minute, drive the pumps, by means 
of toothed gearing, at 63 revolutions per minute. These pumps 
are of very simple but strong construction, single suction and 
double delivery, entailing one suction and one delivery-valve, 
both heavy and both of small lift. The larger portion of the 
plunger has exactly double the cross-sectional area of the smaller 
portion, so that in the forward stroke half of the water taken in 
at the last admission is pumped into the high-pressure mains, and 
at the same time a fresh supply of water is sucked in. During the 



120 TUNNELING 

backward stroke half of this new supply is pumped into the 
mains, and the remainder enters the second chamber, to be 
pumped during the next forward stroke. Thus the work done 
in the two strokes is practically the same. The pumps are in 
pairs, and are set at an angle of 90°, to insure uniform pressure 
and uniform delivery in the mains. Their size varies; but at 
Iselle there are three pairs, with a stroke of 2 ft. 2J ins., and the 
plungers of 2{^ in. and 1| ins. (approximately) in diameter, 
supplying 1.32 gallons per second. 

To avoid injury to the valves, the water to be pumped is 
taken from a stream up the mountain side, and is passed through 
filter screens. The high-pressure water, after passing an ac- 
cumulator, enters the tunnel in solid drawn wrought-iron tubes, 
SJ ins. in internal diameter, ^^ in. thick, and in lengths of 26 ft. 
The diameter of these mains varies with their length, so as to 
avoid loss of pressure. With the 1250 yds. of tunnel now driven 
10 atmospheres are lost. 

At Brigue the installations are, as far as possible, identical. 
The Rhone water, however, before reaching the water-house, 
is carried from the filter basins, a distance of 2 miles, in an 
armored canal built upon the Hennebique system,* the walls 
and supporting beams, of cement concrete, being strengthened 
by internal tie-bars of steel. The concrete struts, resembling 
balks of timber at a distance, are occasionally 35 ft. high and 
1 ft. 7J ins. square. The metallic conduit is 5 ft. in diameter, 
with a minimum flow of 176 cu. ft. per second and a total fall 
of 185 ft. In case water-power should be unavailable, three 
semi-portable steam engines, two of 80 H.P. and one of 60 H.P., 
are always kept in readiness at each end of the tunnel, and are 
geared by belts to the turbine shaft. 

Ventilation. — In tunneling, one of the most important prob- 
lems to be solved is that of ventilation, and it is for this reason 
that the Simplon tunnel consists of two parallel headings with 
cross cuts at intervals of 220 yds. At Brigue, a shaft 164 ft. 

* Network of steel rods embedded in concrete. 



TUNNELS THBOUGH HARD ROCK 121 

deep was sunk through the overlying rock until the '' gallery 
of direction " was encountered. Up this chimney the foul air 
is drawn by wood fires, the fresh air — a volume of 19,000,000 
cu. ft. per day, or 13,200 cu. ft. per minute — entering by head- 
ing No. 2, penetrating up to the last cross gallery, and returning 
by tunnel No. 1. The entrances of No. 1 and the '' gallery 
of direction," besides those of all the intermediate cross galleries, 
are closed by doors. By this arrangement, however, fresh 
air does not reach the working faces; therefore a pipe, 8 ins. 
in diameter, is led from the fresh air in No. 2 to within 15 yds. 
of the face of each heading, and up this pipe a draft of air is 
induced by means of a jet of water, the volume to each face 
being 800 cu. ft. per minute. One single jet of water from the 
high-pressure mains, with a diameter of ^\ in., is capable of 
supplying over 1000 cu. ft. of air per minute at the end of 
160 yds. of pipe, and during the attack the men at the drills 
are in a constant breeze with the thermometer standing at 
70° F. At Iselle, air is blown into the entrance of heading 
No. 2 at the rate of 14,100 cu. ft. per minute by two fans driven 
from the turbine shaft. This air travels from the fans along 
a pipe 18 ins. in diameter, till a point 15 yds. up the tunnel is 
reached, where beyond a door the pipe narrows to form a nozzle 
10 ins. in diameter. This door is kept open to allow the outside 
air to be induced up the tunnel, as the headings are at present 
only 2500 yds. long, giving a resistance of not quite sufficient 
power to cause the air to return. The fresh air then travels up 
No. 2, crossing over the top of the " gallery of direction," from 
which it is shut off by doors, to the last cross gallery, returning 
by No. 1, and finally leaving either by the ''gallery of direction" 
or by No. 1. A system of cooling the air and driving it on by 
means of a large number of water- jets will be installed in No. 2 
where that heading crosses over the " gallery of direction," but 
at present there is no need for it. 

The average temperature at the face is 73° F. during the 
drilling operation, 76° F. after firing the charges, and a max- 



122 TUNNELING 

imum of 80° F., lately attaining to 86° F. on the south side, 
with 80° F. and 85° F. before and after firing. The tempera- 
ture of the rock is taken at every 110 yds. in holes 5 ft. deep, 
and shows a gradual increase according to the depth of over- 
laying rock, to the conductivity of the rock, and to the form of 
the mountain surface. The maximum hitherto reached on the 
north side is 68° F., w^hile on the south side, although a smaller 
distance has been traversed, it attains to 79° F., due to the 
more rapid increase in depth. Moreover, the temperature of 
the rock is observed at the permanent stations, 550 yds. from 
the entrances, in its relation to that of the tunnel and outside 
air, and though on the north side that of the rock varies almost 
as quickly as that of the tunnel air, on the south it is influenced 
very much less. 

A few statistics may be of interest with regard to the prog- 
ress of the last three months (taken from the trimestrial report 
of January, 1900). At Brigue, where there are three drilhng- 
machines in No. 1 and two in the parallel heading, the total 
length excavated was 995 yds. or 6409 cu. yds. in 89 working 
days, the average cross-sectional area being 57 sq. ft. This re- 
quired 507 attacks and 3066 holes, which had a total depth of 
26,600 ft. and 14,700 re-sharpenings of the driUing-tool, with 
44,000 lbs. of dynamite. 

The average time occupied in drilHng was 2 hrs. 45 mins., 
while charging, firing, and clearing away the debris took 6 hrs., 
35 mins. At Brigue 648 men and 29 horses were employed at 
one time in the tunnel. At Iselle the numbers were 496 men 
and 16 horses, working in shifts of 8 hrs. Outside the tunnel, 
in the shops, forges^ etc., the men work 8 hrs. to 11 hrs. per 
day, the total being 541 men at Brigue and 346 men at Iselle. 
On the Italian side, where the rock is very much harder, there 
were three drilHng-machines in each heading; the total length 
excavated, with a cross-sectional area of 62 sq. ft., was 960 yds. 
or 6700 cu. yds. in 91 working days. This required 61,293 
re-sharpened tools, 758 attacks, 7940 holes with a total depth 



TUNNELS THROUGH HARD ROCK 123 

of 33,000 ft., and 56,000 lbs. of dynamite. The average time 
spent in drilling was 2 hrs. 55 mins., and in charging and clear- 
ing 2 hrs. 36 mins. Thus, in the hard gneiss, to excavate 1 cu. 
yd. of rock required 8J lbs. of dynamite, and each tool pierced 
6 J ins. of rock before it required re-sharpening. 

THE MURRAY HILL TUNNEL 

The drift method of excavating tunnels was followed in 
Section IV of the New York Subway, under Park Avenue 
between 33rd and 41st Streets. At this point the four tracks 
of the subway pass under a rocky elevation, known as Murray 
Hill, in two double track parallel tunnels, 43 ft. apart, center to 
center. Here already existed a double track tunnel which was 
built many years ago by the New York Central and Hudson 
River R.R., and is now used by the Madison Avenue surface 
cars. The two subway tunnels were driven close below the 
existing tunnel and also very near the foundations of expensive 
residences along Park Avenue, particularly on Murray Hill, one 
of the best residential sections of the city. 

Material Penetrated. — The material penetrated by the exca- 
vation consisted chiefly of a surface outcrop of the mica-schist 
rock which underlies Manhattan Island. The rock was for the 
most part in compact strata, dipping at about 45° from East 
to West, but at intervals an unstable stratum was encountered 
which when free slid on the underlying stratum. Troubles 
from such slides were experienced during the construction of 
the tunnel. 

Cross-Section. — The cross-section selected for the tunnels 
had vertical side walls and a three-centered roof arch with the 
flattest curve at the crown. The interior dimensions were 
25 ft. wide and 16 ft. high. The selected cross-section was not 
the best suited for a tunnel to be driven through rock, where 
the sharpest curve should be at the top, but in this case the 
flattened curve was chosen because of local conditions; chiefly, 
the presence of the existing tunnel and the consequent neces- 



124 



TUNNELING 




sity of leaving a certain thickness of rock between it and the 
new tunnel, without depressing very much the grade of the 
subway. 

Excavation. — The two parallel tunnels were driven exclu- 
sively from the ends reached by shafts; thus the tunnels were 
attacked at four parts. It was in these tunnels that a compara- 
tive test was made of the different methods of driving tunnels 
through rock. The contractor applied the heading and drift 
method at the southern ends of the tunnels, the eastern tunnel 
being driven by means of a drift while in the western tunnel 
the usual heading method was followed. This latter method 
is illustrated in the chapter following and the eastern tunnel at 
33rd Street, excavated by means of a drift, is here considered. 

Fig. 58 shows the sequence of 
cuts adopted for this tunnel. It 
was begun by a bottom drift, about 
10 ft high, 8 ft. wide and 7 ft. deep, 
which was located at one side of 
the axis of the tunnel, as indicated 
in the figure. This drift was imme- 
diately widened by removing the 
portions marked 2. About 50 ft. 
in the rear the part marked 3 was 
taken away, thus clearing the entire lower portion of the tun- 
nel. Section 4, about 50 ft. to the rear of section 3, was then 
broken down and removed. 

The methods of drilling and blasting were as follows: In 
taking out the original drift, a wedge-shaped center cut was made 
and then enlarged to the full size of the drift by drilling parallel 
holes. The succeeding sections, 2 and 3, were removed by 
driving parallel holes, while the top section, 4, was taken away 
by a center cut and parallel holes. The drills were mounted 
on columns, two drills to a column, and the holes were usually 
drilled about 7 ft. deep, starting with a diameter of 2f in. and 
ending with a diameter of If in. They were blasted with 40% 



Fig. 58. — 'Sequence of Excavation in 
the Murray Hill Tunnel. 



TUNNELS THROUGH HARD ROCK 



125 




Fig. 59. — Traveling Platform for the Excavation of 
the Upper Side of the Murray Hill Tunnel. 



dynamite in light charges, only a few holes being fired at a time, 
usually not more than three or four. 

To remove section 4, a traveling platform 10 J ft. long and 
25 ft. wide was used. This platform, as shown in Fig. 59, con- 
sisted of two longitudinal 
beams mounted on four 
double flanged wheels 
which wTre running on 
tracks laid 23 ft. apart. 
Resting on top of these 
beams were four 12 in. X 
12 in. uprights braced in 
every direction against the 
framework of the platform. 
This frame was built of 
12 in. X 12 in. beams laid 

longitudinally, the transverse beams being 12 in. X 14 ins. The 
platform proper was made of 3 in. planks, and was set 9 ft. above 
the tunnel floor. The columns supporting the drills for the exca- 
vation of the upper section 4, were set up above the platform 
which was then reinforced by other vertical props, as indicated 
by the dotted lines in the figure. These props, however, were 
placed so as to leave a clearance beneath the platform for the 
cars to carry away the debris from the front. During the 
blasting the platform was moved back so that the blasted rock 
fell to the floor of the tunnel, whence it was loaded into boxes 
on the cars. 

Strutting. — When the rock was seamy and full of fissures, 
running in every direction, it was necessary to support the 
roof of the excavation. This was done in the following manner : 
After part 4 was removed the timbers supporting the roof of 
the excavation were set up. In this case, the polygonal strutting 
was used. This consisted of heavy timber frames placed trans- 
versely to the axis of the tunnel and supporting the planks or 
poling-boards which ran longitudinally against the roof of the 



126 



TUNNELING 




excavation. The seven-segment arch frame was used in the 
Murray Hill tunnel. At the bottom of part 4 were placed 
longitudinally 12 X 16 in. beams and upon them rested the 
inchned segments which, with a horizontal one, formed the 

arch frame as shown in Fig. 60. 
When the pressures were too 
heavy the crown segment was 
reinforced by a 6 X 12 in. beam, 
kept in place by two 12 X 12 in. 
inchned props which rested on 
the templates. As the tunnel 
was lined with concrete, the tim- 
bering was left in place and it 

Fig. 60. -Timberin^g^Used in the Murray ^^g ^^-j^ OUtslde the Me of the 

extrados of the concrete lining. 
Timbering was only used for a short distance but it necessitated 
a larger amount, of rock excavation when it was required. 

Hauling. — Great efficiency was shown in the method of 
hauling away the excavated materials. Three narrow-gauge 
parallel tracks were laid on the floor of the tunnel and extended 
to the faces of the advance drifts. Small flat cars were run on 
these tracks. They carried steel boxes, 5 ft. square and 15 ins. 
deep, fitted with three lifting rings and chains. AVhen filled, 
the cars were run to the bottom of the shaft, the boxes were 
hoisted by a stiff-legged derrick placed at the shaft head, and 
the debris was dumped into storage bins of 300 cu. yds. capacity. 
These bins were elevated 8 ft. above the street so that the 
wagons could be driven under it to take loads of spoil by 
means of chutes. The broken rock was loaded into the boxes 
by hand. 

Concrete Lining. — The tunnel was lined with concrete which 
was manufactured by a quite elaborate plant. A stone crushing 
plant, consisting of bins for raw and crushed stone, was erected 
at the shaft head and a mixing plant was suspended from the 
shaft. On the platform of the shaft head were two bins side 



TUNNELS THROUGH HARD ROCK 127 

by side, one for crushed stone, the other for sand; both of which 
communicated, by means of trap doors, with a hopper chute. 
The materials from the hopper were dehvered into a measuring 
box where cement was laid on top of the other ingredients by 
hand. They were then conveyed through a canvas chute into 
a cubical mixer operated by an engine. The mixer discharged 
its contents into skips set on cars at the bottom of the 
shaft and the concrete was hauled inside the tunnel ready for 
use. 

The construction of the lining was accomplished by means of 
traveling platforms. The footing courses were laid first. Be- 
cause these projected inward about 18 ins. from the faces of the 
finished sidewalks it was possible to lay a track rail on their top 
inner edges on each side of the tunnel. These track rails carried 
the traveling platforms. There were three of these platforms; 
the forward one was used for building the side walls; the center 
one, for carrying a derrick; the last one, for building the roof 
arch. The side wall platform was mounted on six wheels. On 
each side there was mounted an adjustable lagging which was 
curved to conform to the inside profile of the side wall. In 
operation this platform was run to the point where the side walls 
were to be constructed and the lagging was adjusted to position 
and fastened. Skips of concrete were then hoisted on its top, 
their contents were shoveled into the space between the lagging 
and the wall of the excavation and were there rammed into place 
until the finished concrete had reached the top of the lagging. 
When the concrete had set, the wedges holding the lagging in 
place were loosened and the platform was moved ahead and 
adjusted for building a new section of wall. The derrick plat- 
form was 23J ft. wide and 18 ft. long. Transversely, it had 
three bays, two of which were floored over and one was left 
without flooring to allow passage for the concrete skips to and 
from the cars, on the tunnel floor beneath. At the center of 
the floored area was mounted a derrick to handle the skips. In 
operation, the derrick platform came between the side wall 



128 TUNNELING 

platform ahead and the roof platform behind. The construction 
of the roof platform was practically the same as the side wall 
platform with the addition of roof arch centers at each bent 
on which lagging could be placed. The mode of procedure was 
to erect the form for a small space between the side walls already 
built and the haunches of the center, to shovel concrete from the 
skips and to run it into place. Then the roof lagging, a part at 
a time, was placed upward from the haunches and the concrete 
was filled and rammed behind it. The lining was built from the 
haunches upward until the two sides approached within a distance 
of about 5 ft. from each other at the crown. This 5 ft. crown 
strip or key was built by working from the rear toward the front 
end of the platform. 

Plant. — The plant used by the contractors for Section IV. 
of the subway comprised a central power plant located, about 
4000 ft. from the work. This was on 42nd Street near the East 
River and furnished power for the work on both Sections IV. 
and V. The buildings consisted of an engine room 63 X 30 ft. 
and a boiler room, 42 X 28 ft. In the former room was located 
one Rand-Corliss air compressor, 22 X 40 X 48 ins., having a 
capacity of 5000 cu. ft. of free air per minute; in the latter room 
there were two 200 H.P. water tube boilers. There were also 
the necessary equipment of feed water pump, air condenser 
pump, etc. The compressors discharged into a 20 X SJ ft. 
receiver of riveted steel through a 7 in. pipe. The air from the 
receiver was carried by a 10 in. pipe 3.277 ft. to the corner of 
Park Avenue and 41st Street, and was thence run south along 
Park Avenue in an 8 in. pipe, from which 3 in. branches led to 
the four headings of the work. 

Ventilation. — The ventilation of the tunnel caused very 
little trouble. In cool weather the natural draft of the shafts 
and the air discharged from the drills served to keep the at- 
mosphere wholesome. In warm weather, artificial means were 
necessary to clear the workings of foul air, particularly after 
blasting. They comprised at each end a 4 ft. American exhaust 



TUNNELS THROUGH HARD ROCK 129 

fan drawing air from a 12 in. riveted galvanized iron pipe, which 
extended to the working faces. 

lUumination. — The tunnel was lighted by electric lamps which 
extended even to the working face. During the blasting, how- 
ever, all the lamps and wires within 100 ft. from the front were 
removed and gasoline torches were used; they were also em- 
ployed before the electric lamps and wires could be replaced, to 
light the tunnel during the operation of clearing the debris. 



130 TUNNELING 



CHAPTER XI. 

TUNNELS THROUGH HARD ROCK (Continued). 
EXCAVATION BY HEADINGS. 



EUROPEAN AND AMERICAN METHODS. 

The more common method of tunneling through hard rock 
is to begin the work by a heading, instead of by a drift. This 
heading may be of small dimensions, and the remainder of the 
section may also be removed in successive small parts, or it may 
be the full width of the section, and the enlargement of the 
section be made in one other cut. 

General Discussion. — When the tunnel is excavated by means, 
of several cuts, which is the method usually employed in 
Europe, the sequence of work is as indicated by Fig. 58. 
Work is begun by driving the center top heading No 1, whose 
floor is at the level of the bottom of the roof arch, and which is 
usually excavated by the circular cut method. This heading is 
widened by removing parts Nos. 2 and 3 until the top part of the 
section is removed, then the roof arch is built with its feet rest- 
ing on the unexcavated rock below. The lower portion of the 
section or bench is removed by first sinking the trench No. 4, 
after which part No. 5 is taken out, and then parts Nos. 6 and 7, 
and the side walls built. Part No. 8 for the culvert is finally 
opened. The heading is, as a rule, driven far in advance, but 
the excavation of each of the other parts follows the preceding 
one at a distance behind of about 300 ft. 

The strutting, when any is required, is usually the typical 
radial strutting of the Belgian method of tunneling. The 
masonry lining is constructed practically the same as in tunnels 
excavated by a drift. The hauling is done on a single track 
laid in the heading No. 1, which separates into double tracks. 



TUNNELS THROUGH HARD ROCK 131 

where the full top section has been excavated by the removal 
of parts No. 2. These two tracks are again combined and form 
a single track along the top of part No. 5, which has been left 
wider than part No. 4 for this particular purpose. When part 
No. 3 is excavated a standard-gauge track is laid on its floor ; 
and as the full section of the tunnel is completed by taking out 
parts Nos. 4 and 5, this single track is replaced by two standard- 
gauge tracks, into which it switches. Spoil is transferred from 
the narrow-gauge tracks on the upper level, to the standard- 
gauge tracks on the tunnel floor, by means of chutes, and build- 
ing material is transferred in the opposite direction by means of 
hoisting apparatus. 

When the excavation is made by a single wide heading, and 
a single other cut for removing the bench, which is the method 
preferred by American engineers, it is called the Heading and 
Bench method. The work begins by removing a top heading 
the full width of the section; this heading is usually made 7 ft. 
or 8 ft. high, and is excavated by the center cut method. The 
method of strutting usually employed is to erect successive 
three- or five-segment timber arches, whose feet rest on the 
top of the bench; when the bench is removed, posts are inserted 
under the feet of each arch. These arches are covered with a 
lagging of plank. In America it has often been the practice to 
let this strutting serve as a temporary lining, and to replace 
it only after some time, often after years, with a permanent 
lining of masonry. In a succeeding chapter, some of the methods 
adopted in relining timber-lined arches with masonry are de- 
scribed. The hauling is done by either narrow or broad gauge 
tracks laid on the floor of the completed section below. A device 
called a bench carriage is often employed to enable the cars 
running on the heading tracks to dump their loads into the cars 
below, without interfering with the work on the bench front. 
This device consists of a wide platform carried on trucks, running 
on rails at the sides of the tunnel floor, so that it is level with 
the floor of the heading. The front of this platform carries a 



132 



TUNNELING 



hinged leaf which may be raised and lowered, and which forms 
a sort of gang-plank reaching to the floor of the heading. By 
running the heading cars out on to this traveling platform, they 
can be dumped into the cars below entirely clear of the work in 
progress on the bench front. 

For the purpose of illustrating the two methods of driving 
tunnels by a heading, which have been briefly described, the St. 
Gothard and the Fort George tunnels have been selected. The 
St. Gothard tunnel is selected, as being one of the longest tunnels 
in the world, and because it was excavated by a number of small 
parts ; and the Fort George tunnel, as being a double-track tunnel, 
driven by a heading, and bench, and having a concrete lining. 

ST. GOTHARD TUNNEL. 

The -St. Gothard tunnel penetrates the Alps between Italy 
and France, and is 9^ miles long. It was constructed in 1872-82. 
Material Penetrated. — The St. Gothard tunnel was excavated 
through rock, consisting chiefly of gneiss, mica-schist, serpen- 
tine, and hornblende, the strata having an inclination of from 

45° to 90°. At many points the 
rock was fissured, and disintegrated 
easily, and water was encountered 
in large quantities, causing much 
trouble. 

Excavation. — The sequence of ex- 
cavation is shown by Fig. 14, p. 36. 
First the top center heading, No. 1, 
whose dimensions varied from 8.25 X 
8.6 ft. to 8.5X9 ft., according to the 
quality of the rock, was driven 
never less than 1000 ft. and some- 
times over 3000 ft. in advance of parts No. 2. The exca- 
vation of parts No. 2 opened up the full top section, and parts 
Nos. 3, 4, 5, 6, and 7, were removed in the order numbered. 

Strntting. — Where regular strutting was required, the con- 
struction shown in Fig. 62 was adopted. 



5 2 

4r- 



Fig. 61. — Diagram Showing Se- 
quence of Excavation in Heading 
Method of Tunneling Rock. 



TUNNELS THROUGH HARD ROCK 133 

Masonry. — The St. Gothard tunnel is lined throughout with 
masonry. After the upper portion of the section was fully 
excavated, the roof arch was built with its feet resting upon 
short planks on the top of the bench. Plank centers were used 
in constructing the arch. For the arch brick masonry was 
employed, but the side walls were built of rubble masonry. 
Shelter niches, about 3 ft. deep, were built into the side walls 
at intervals, and about every 3,000 ft. storage niches about 10 
ft. deep, and closed with a door, were constructed. The cul- 
vert was of brick masonry. 

Mechanical Installation. — Water-power was used exclusively 
in driving the St. Gothard tunnel. At the north end, the 
Reuss, and at the south end, the Tessin and the Tremola, rivers 
or torrents were dammed, and their waters conducted to tur- 
bine plants at the opposite ends of the tunnel. The power thus 
furnished by the Reuss was about 1,500 H.P., and the power 
furnished by the combined supply of the Tessin and Tremola 
was 1,220 H.P. The turbine plant at both ends at first con- 
sisted of four horizontal impulse turbines, but later, two more 
turbiues were added at the south end. Each of the two sets of 
four turbines first installed drove five groups of three compres- 
sors each, and the two supplementary turbines drove two groups 
of four compressors each. The compressors were of the Colladon 
type with water injection, and four groups of three compressors 
each were capable of furnishing 1,000 cu. yds. of air compressed 
to between seven and eight atmospheres every hour, or about 
100 H.P. per hour, delivered to the drills at the front. This 
air when exhausted provided about 8,000 cu. yds. of fresh air 
per hour for ventilation. 

The compressors at each entrance discharged into a group 
of four cylindrical receivers of wrought-iron each 5.3 ft. in 
diameter by 29.5 ft. long, and having a capacity of 593 cu. ft. 
The cylinders were placed horizontally, the first one receiving 
the air at one end and discharging it at the other end into the 
next cylinder, and so on. By this arrangement the air was 



134 TUNNELU^TG 

drained of its moisture, and the discharge from the end receiver 
into the tunnel delivery pipes was not affected by the pulsations 
of the compressors. The delivery pipe decreased from 8 in. 
in diameter at the receiver to 4 ins. in diameter, and finally to 
2i. ins. in diameter, at the front. 

The drills employed were of various patterns. The first one 
employed was the Dubois & Frangois " perforator," in which the 
drill-bit was fed forward by hand. This was replaced by Fer- 
roux drills having an automatic feed. Jules McKean's "perfo- 
rator " was employed at the north end of the tunnel. All of 
these drills were of the percussion type, and were mounted on 
carriages running on tracks. Their comparative efficiency was. 
officially tested in drilling granitic gneiss with an operating 
air pressure of 5.5 atmospheres with the following results : 

Name of Drill. Penetration Ins. per Min. 

Ferroux 1.6 

McKean 1.4 

Dubois & Frangois 1.04 

Soummelier 0.85 

The heading was excavated by the circular cut method, the 
holes being driven as follows : Near the center of the heading 
three holes were first drilled, converging so as to inclose a 
pyramid with a triangular base. Around these center holes. 
from 9 to 13 others were driven parallel to the tunnel axis. 
The center holes were blasted first, and then the surrounding 
holes. From 3 to 5 hours were required to drill the two sets 
of holes, and from three to four hours were required to remove 
the blasted rock. The number of holes drilled in removing 
each of the various parts was as follows : 

Part No. 1 6 to 9 

Part No. 2 6 to 10 

Part No. 3 ^ 2 

Part No. 4 . . . . . . . ' 6 to 9 

Part No. 5 3 

Part No. 6 6 to 9 

Part No. 7 1 

Total for full section 36 to 40 



TUNNELS THROUGH HARD ROCK 



135 



Hauling. — Two different systems were employed for haul- 
ing the spoil and construction material in the St. Gothard 
tunnel. To remove the spoil from parts Nos. 1 and 2 a narrow- 
gauge track was laid on the floor of the heading, and the cars 
were hauled by horses, the grade being descending from the 
fronts. These narrow-gauge cars were dumped into larger 
broad-gauge cars running on the track laid on the floor of the 
completed section and hauled by compressed air locomotives 
(Fig. 63). To raise the incoming structural material from the 
broad-gauge cars to the narrow-gauge cars running on the level 
above, hoisting devices were employed. 





Fig. 62. — Method of Strutting Roof, 
St. Gothard Tunnel. 



■Fig. 63. — Sketch Showing Arrangement of 
Car Tracks, St. Gothard Tunnel. 



FORT GEORGE TUNNEL.* 



From a point north of 157th Street and Broadway almost to 
Dyckman Street, that is, a distance of nearly two miles, the New 
York Subway passes under an elevation known as Fort Washing- 
ton Heights, which almost bounds Manhattan Island at its upper 
end near the Harlem Ship Canal. Under this elevation the 
rapid transit railroad was constructed in tunnel. The tunnel 
was driven from two intermediate shafts over 110 ft. deep, 
located one at 169th Street and the other at 181st Street and 

* Condensed from a paper by Stephen W. Hopkins in Harvard Engineering Journal, 
April, '08. 



136 TUNNELING 

Broadway. Both shafts were sunk at one side of the center 
line of the tunnel. After these shafts had been utiUzed for 
working purposes during the construction of the tunnel, they 
were equipped with electric elevators to carry passengers from 
the streets to the deep station. 

Material. — The material encountered in the excavation of the 
Fort George tunnel was the usual mica schist met everywhere 
on Manhattan Island. It was full of seams with strata running 
in every direction to such an extent that at many points the roof 
of the tunnel had to be supported by timbers; at other parts 
along the Hne the rock was so disintegrated that it was considered 
a very loose and treacherous soil. Two serious accidents, each 
accompanied by loss of life, occurred during the construction of 
this tunnel. Both of them were caused by the sudden fall of 
a large ledge of rock which, after the tunnel had been excavated 
to the full section, remained hanging on the roof, deprived of 
any support and held in place by the little cohesion of the material 
packing the seams. 

Excavation. — The tunnel was excavated by the heading 
method in only two cuts, viz., the heading and bench as indicated 
in the Fig. 63. The heading, almost as wide as the upper portion 
of the tunnel section, was excavated in the manner explained on 
page 91. After the heading was removed, the enlargement of 
the entire upper section of the tunnel was accomphshed by 
driving three inclined holes at each side of the heading. They 
were driven at different depths and inchnations, as shown in 
the figure and were called trimming holes. At the same time 
the bench was removed by means of five holes — three vertical 
and two inclined. The line of subgrade was reached by means 
of five grading holes driven almost horizontal with a shght 
inclination downward. The air drills for the heading were 
mounted on columns, all the others on tripods. The blasting 
was done in the following order: the grading holes were blasted 
in the first round, the bench and trimming in the second, the 
center cut of the heading in the third, the sides in the fourth 



TUNNELS THROUGH HARD ROCK 



137 



and the dry holes in the last. Thus each advance of 7 ft. of 
the whole tunnel section was made by means of forty holes fired 
in five rounds which consumed 277 lbs. of dynamite with an 




Cross. Section. 

Fig. 64. — Arrangement of Drill Holes in 

the Fort George Tunnel. 



Longitudinal Section. 

Fig. 65. — Longitudinal Section of the Heading 
and Bench Excavation at the Fort George 
Tunnel. 



average additional quantity of 76 lbs., making a total of 353 lbs. 
With the exception of the center cut, where 60% dynamite was 
used, all the other holes were discharged with 40% dynamite. 

Strutting. — When the rock was of such a character as to be 
dangerous and required permanent timber support, until the 
masonry lining was in place, the method employed was as follows : 
a top heading was first excavated about 10 ft. deep and from 10 ft. 
to 12 ft. wide for some distance, 100 ft. to 500 ft., the dangerous 
rock being supported by 10 X 10 in. yellow pine plumb or raking 
posts and sometimes by timber bents {" caps and legs "). The 
next process was to widen the heading to the full width of 30 ft. 
for a length of about 20 ft., placing timber supports under the 
dangerous rock as the widening-out progressed. The excava- 
tion was deepened a little at the sides to 9.5 ft. below the roof 
grade (ordered line of excavation) or about 11 ft. below the 
roof grade, which was necessary when segmental timbering was 
to be used, to allow for placing a 12 X 12 in. " wall plate " 
(timber sill) along each side. These wall plates, generally 20 ft. 
long, were set to the correct elevation and were leveled by 
blocking and wedging. As soon as the wall plates were set, 



138 TUNNELING 

the work of erecting the segmental timber sets, one set at a time, 
was begun by starting from the wall plates and supporting the 
timber on scaffolding until keyed in, then it was blocked up to 
the rock at each joint and at other necessary points. When two 
or more sets were erected, lagging, made of boards 2 ins. thick 
by 6 to 10 ins. wide, was placed over the segmental timber " sets '' 
and the space above the timber dry packed with small stone 
placed by hand. Sometimes there was enough room between the 
timber and the rock to do all the dry packing after the full 
number of sets, generally six, had been placed on the two wall 
plates. The temporary timber posts and braces were taken out 
as the segmental timber sets were erected. 

The seven timbers that made up a timber set were of yellow 
pine each 10 X 10 ins., 5 ft. 2 ins. long at the intrados and 5 ft. 
6 ins. at the extrados. The sets were spaced from 3 ft. to 5 ft. 
apart, but generally 3.5 ft. and braced to each other at each joint 
of the segmental timbers by 6 X 8 in. spreaders which were 
wedged against the joint sphces. 

When the timbers w^ere all erected on a set of wall plates 
(20 ft.) and the lagging and dry packing were completed the 
work of taking out the bench, which had been partly drilled as 
the timber sets were erected, was resumed. The face of the 
bench, which had been left about 4 ft. from the end of the pre- 
vious set of wall plates, was brought forward slowly by placing 
10 X 10 in. plumb posts which extended below subgrade under 
the wall plates. These posts were generally spaced the same 
as the timber sets above and directly under them. 

When the face of the bench had been brought to within 3 or 
4 ft. of the forward end of the wall plate, the process of widening 
out and timbering another 20 ft. length of heading was begun. 
In some places the rock, though needing permanent support, 
was such that the work of taking out the bench and widening 
the heading was carried on simultaneously without increasing 
the danger; but the greater portion of the work, when strutting 
was required, was done as has been described. 



TUNNELS THROUGH HARD ROCK 139 

Hauling. — The excavated material was loaded at the foot 
of the bench in dump cars which were run by mule power to the 
portal or the shaft according to location, on 36 in. gauge-service 
tracks. Inclines at 159th Street were graded from the portal at 
158th Street to the street surface. The cars were formed at 
this portal into a train and were taken up the incHne to the dump 
at 162nd Street and the North River by construction locomotives. 
At the 168th Street and 181st Street shafts, the cars were hoisted 
to the surface in cages (elevators). In the former case, they were 
taken to the dump at 165th Street and the North River by mules 
and gravity; in the latter case, to various dumps by teams. 
At both shafts, stone crushers were located, therefore a great 
part of the material did not have to be hauled to the dumps 
or even taken to the surface as a great deal of stone was used in 
dry packing over the concrete arch. The material from the 
portal at Fort George was hauled by mules directly to the dump 
near by. 

Lining. — The entire tunnel was lined with concrete, consisting 
of a floor 4 ins. thick and vertical side walls 18 ins. thick and 
25 ft. apart, which carried a semicircular arch 18 ins. thick 
except in the timbered portions where the thickness was in- 
creased to 21 ins. and to 24 and 27 ins. in some places. The 
springing line of the arch is 6 ft. 2 ins. above the concrete floor 
(5 ft. 6 ins. above the base of rail), hence the maximum clearance 
above the base of rail is 18 ft. The side walls and arch were 
built solid of rock to a height of 8 ft. above springing hne and 
the space above that point between the concrete and the rock 
was packed by hand with small stones. The concrete of the 
arch was laid on timber centers erected for that purpose. 

The heading and bench method of excavating rock tunnels 
is not always followed in the manner just described but is em- 
ployed with slight modifications. There is a large variety of 
modifications but only the two most commonly used in practical 
works are given here. The heading and bench method illus- 
trated in Fig. 66 was used, among others, on the Gallitsin 



140 



TUNNELING 




tunnel along the Pennsylvania R.R. at the summit of the 

Alleghenies near Altoona, Pa., and more recently in the tunnels 

constructed by the same company under Bergen Hill, N. J., for 

the entrance to New York City. The 

shape of the cross-section of these tunnels 

was semicircular arch on vertical side 

walls. The excavation was made in three 

consecutive cuts, viz., the heading marked 

1 in the figure, the top bench 2, and the 

lower bench 3. A heading 7 ft. high and 

10 ft. wide was attached near the crown 

of the arch and the rock was removed by 

means of a center cut and parallel side 

Fig. 66.- Diagram Showing holes, the number of holes depending upon 

HoiefTnThTHeadtg^and ^he cousisteucy of the rock. The part 

Bench of the Gaiiitsin Tun- ;^q^ 2 was excavatcd by drilling holes at 

nel. *^ ° 

each side to cUfferent depths and at dif- 
ferent inclinations in order to reach the Hne of the profile as 
well as the springing line of the proposed tunnel. The central 
part of the top bench was excavated by means of holes driven 
vertically from the floor of the heachng. The bottom bench 
No. 3, included between the spring- 
ing hne of the arch and subgrade, 
was removed by means of five ver- 
tical holes driven from the floor of 
the top bench. The three different 
working parts were kept nearly 
10 ft. apart. Blasting was effected 
in reversed order to the figures 
marked in the diagram, viz., the 
bottom bench first and the heading 
last. 

Still another modification of the heading and bench method, 
commonly followed by American engineers, is the one shown in 
Fig. 67. This consists in dividing the tunnel section in three 




Fig. 67. — Diagram Showing a 'Modi- 
fication of the [Heading and Bench 
Method. 



TUNNELS THROUGH HARD ROCK 141 

parts by horizontal lines. The resultant parts are first the 
heading excavated close to the roof, and as wide as the whole 
section of the tunnel; second, the top bench in the middle, and 
lastly the bottom bench excavated to the depth of the pro- 
posed tunnel floor. The excavation proceeds in the numerical 
order, beginning at the heading which was excavated, as usual, 
by means of a center cut and side holes to the full width of the 
proposed tunnel. First the top bench, then the bottom bench, 
are removed by means of vertical holes driven from the floor 
of the heading and the floor of the top bench, respectively. 

COMPARISON OF METHODS. 

The differences between the drift and heading methods of 
excavating tunnels through rock, consist chiefly in the excava- 
tions, strutting, and hauling. When the drift method is em- 
ployed an advanced gallery is opened along the floor of the 
tunnel before the upper part of the section is removed, and 
when the heading method is employed the upper part of the 
section is completely excavated before any part of the section 
below is excavated. When the drift method of driving is em- 
ployed polygonal strutting is usually used, and longitudinal 
strutting is employed with the heading method of driving. In 
the drift method the hauling is done by one system of tracks at 
the same level, while in the heading method two systems of 
tracks are employed at different levels. 

It is, perhaps, impossible to state without qualification which 
method is the better. European engineers who have been con- 
nected with both the Mont Cenis and St. Gothard tunnels, driven 
by the drift and heading methods respectively, had the oppor- 
tunity to practically observe the advantages and disadvantages 
of these two methods. Their conclusion was that the drift 
method was more convenient for tunnels driven through hard 
and compact rock, and that the heading method was better for 
tunnels of fissured and disintegrated rocks. To prove this 
opinion, experiments were made in one of the tunnels approach- 



142 TUNNELING 

ing the great St. Gothard tunnel. On a short tunnel the exca- 
vation was made by the drift method from one portal, while at 
the other, the heading method was followed. Although the 
general rule was fully confirmed still the conditions at the portals 
were not identical. More conclusive experiments were made by 
Mr. Ira A. Shaler, the contractor for Section IV., of New York 
Rapid Transit Railway. He had the opportunity of driving two 
parallel tunnels under Murray Hill only 17 ft. apart. The 
eastern tunnel was driven by the drift method, the western one 
by the heading method. After the work had proceeded for a 
few months, Mr. Shaler stated that in his case the drift method 
was more convenient. He could spare drilling several holes 
at each advance, thus obtaining economy in time, labor and 
material without considering the advantage of a simpler trans- 
portation- of the debris. He promised to pubhsh his results 
for the benefit of the profession, but, unfortunately, lost his 
life in an accident in the tunnel before the completion of the 
work. 

An advantage that the drift method affords in long tunnels is, 
that the water, which is usually found in large quantities under 
high mountains, is easily collected in the drift and conveyed to 
the culvert, while in the heading method the water from the 
advance gallery, before being collected into the culvert built 
on the floor of the tunnel, must pass through all the workings. 
This may be a serious inconvenience when water is found in 
large quantities, as, for instance, was the case in the St. 
Gothard tunnel, where the stream amounted to 57 gallons per 
second. 



TUNNELS THROUGH SOFT GROUND 143 



CHAPTER XIL 

EXCAVATING TUNNELS THROUGH SOFT 

GROUND ; GENERAL DISCUSSION ; THE 

BELGIAN METHOD. 



GENERAL DISCUSSION. 

It may be set down as a general truth that the excavation 
of tunnels through soft ground is the most difficult task which 
confronts the tunnel engineer. Under the general term of soft 
ground, however, a great variety of materials is included, be- 
ginning with stratified soft rock and the most stable sands and 
clays, and ending with laminated clay of the worst character. 
From this it is evident that certain kinds of soft-ground 
tunneling may be less difficult than the tunneling of rock, 
and that other kinds may present almost insurmountable dif- 
ficulties. Classing both the easy and the difficult materials 
together, however, the accuracy of the statement first made 
holds good in a general way. Whatever the opinion may be 
in regard to this point, however, there is no chance for dispute 
in the statement that the difficulty of tunneling the softer and 
more treacherous clays, peats, and sands is greater than that 
of tunneling firm soils and rock ; and if we describe the methods 
which are used successfully in tunneling very unstable materials, 
no difficulty need be experienced in modifying them to handle 
stable materials. 

Characteristics of Soft-Ground Tunneling. — The principal char- 
acteristics which distinguish soft-ground tunneling are, first, 
that the material is excavated without the use of explosives, 
and second, that the excavation has to be strutted practically 



144 



TUNNELING 



as fast as it is completed. In treacherous soils the excavation 
also presents other characteristic phenomena: The material 
forming the walls of the excavation tends to cave and slide. 
This tendency may develop immediately upon excavation, or it 
may be of slower growth, due to weathering and other nat- 
ural causes. In either case the roof of the excavations tends 
to fall, the sides tend to cave inward and squeeze together, and 
the bottom tends to bulge or swell upward. In materials of 
very unstable character these movements exert enormous pres- 
sures upon the timbering or strutting, and in especially bad 
cases may destroy and crush the strutting completely. Out- 
side the tunnel the surface of the ground above sinks for a con- 
siderable distance on each side of the line of the tunnel. 

Methods of Soft-Ground Tunneling. — There are a variety of 
methods of tunneling through soft ground. Some of tjiese, 
like the quicksand method and the shield method, differ in char- 
acter entirely, while in others, like the Belgian, German, Eng- 
lish, Austrian, and Italian methods, the difference consists 
simply in the different order in which the drifts and headings 
are driven, in the difference in the number and size of these 
advance galleries, and in the different forms of strutting frame- 
work employed. In this book the shield method is considered 
individually ; but the description of the Belgian, German, Eng- 
lish, Austrian, Italian, and quicksand methods are grouped 
together in this and the three succeeding chapters to permit of 
easy comparison. 

THE BELGIAN METHOD OF TUNNELING THROUGH SOFT 

GROUND. 

The Belgian method of tunneling through soft ground was 
first employed in 1828 in excavating the Charleroy tunnel of 
the Brussels-Charleroy Canal in Belgium, and it takes its name 
from the country in which it originated. The distinctive char- 
acteristic of the method is the construction of the roof arcb 



TUNNELS THROUGH SOFT GROUND 



145 



before the side walls and invert are built. The excavation, 
therefore, begins with the driving of a top center heading 
which is enlarged until the whole of the section above the 
springing lines of the arch is opened. Various modifications 
of the method have been developed, and some of the more 
important of these will be described farther on, but we shall 
begin its consideration here by describing first the original and 
usual mode of procedure. 

Excavation. — Fig. 68 is the excavation diagram of the Bel- 
gian method of tunneling. The excavation is begun by open- 
ing the center top heading No. 1, which is carried ahead a 
greater or less distance, depending upon the nature of the soil, 
and is immediately strutted. This heading is then deepened 



\ / 2 Z 

2 \ I 

5 4 5 4 3 4 



Figs. 68 and 68A. — Diagrams Showing Sequence of Excavations in the Belgian Method. 



by excavating part No. 2, to a depth corresponding to the 
springing lines of the roof arch. The next step is to remove 
the two side sections No. 3, by attacking them at the two fronts 
and at the sides with four gangs of excavators. The regularity 
and efficiency of the mode of procedure described consist in 
adopting such dimensions for these several parts of the section 
that each will be excavated at the same rate of speed. When 
the upper part of the section has been excavated as described, 
the roof arch is built, with its feet supported by the unexca- 
vated earth below. This portion of the section is excavated by 
taking out first the central trench No. 4 to the depth of the 
bottom of the tunnel, and then by removing the two side parts 
No. 5. As these side parts No. 5 have to support the arch, 



146 TUNNELING 

they have to be excavated in such a way as not to endanger it. 
At intervals along the central trench No. 4, transverse or side 
trenches about 2 ft. wide are excavated on both sides, and 
struts are inserted to support the masonry previously supported 
by the earth which has been removed. The next step is to 
widen these side trenches, and insert struts until all of the 
material in parts No. 5 is taken out. 

When the material penetrated is firm enough to permit, the 
plan of excavation illustrated by the diagram, Fig. 68A, is substi- 
tuted for the more typical one just described. The only differ- 
ence in the two methods consists in the plan of excavating the 
upper part of the profile, which in the second method consists 
in driving first the center top heading No. 1, and then in tak- 
ing out the remainder of the section above the springing hues 
of the arch in one operation, while in the first method it is done 
in two operations. The distance ahead of the masonry to 
which the various parts can be driven varies from 10 ft. to, in 
some cases, 100 ft., being very short in treacherous ground, and 
longer the more stable the material is. 

Strutting The longitudinal method of strutting, with the 

poling-boards running transversely of the tunnel, is always 
employed in the Belgian method of tunneling. In driving the 
first center top heading, pairs of vertical posts carrying a trans- 
verse cap-piece are erected at intervals. On these cap-pieces 
are carried two longitudinal bars, which in turn support the 
saddle planks. As fast as part No. 2, Fig. 68, is excavated, 
the vertical posts are replaced by the batter posts A and B, 
Fig. 69. The excavation of parts No. 3 is begun at the top, 
the poling-boards a and b being inserted as the work pro- 
gresses. To support the outer ends of these poling-boards, the 
longitudinals X and Y are inserted and supported by the batter 
posts O and D. In exactly the same way the poling-boards c 
and dy the longitudinals V and W, and the struts U and F, are 
placed in position ; and this procedure is repeated until the 
whole top part of the section is strutted, as shown by Fig. 63, 



TUNNELS THROUGH SOFT GROUND 



147 



the cross struts x^ y, 2, etc., being inserted to hold the radial 
struts firmly in position. The feet of the various radial 
props rest on the sill M N. These fan-like timber structures 
are set up at intervals of from 3 ft. to 6 ft., depending upon 
the quality of the soil penetrated. 




Fig. 69.— Sketch Showing Radial Roof Strutting, Belgian Method. 

Centers. — Either plank or trussed centers may be employed 
in laying the roof arch in the Belgian method, but the form of 
center commonly employed is a trussed center constructed as 
shown by Fig. 70. It may be said to consist of a king-post 
truss carried on top of a modified form of queen-post truss. 
The collar-beam and the tie-beam of the queen-post truss are 

spaced about 7 ft. apart, and 

the posts themselves are left far 
enough apart to allow the pas- 
sage of workmen and cars be- 
tween them. The tie beam of 
the king-post truss is clamped 
to the collar-beam of the queen- 
post truss by iron bands. On 
the rafters of the two trusses are fastened timbers, with their 
outer edges cut to the curve of the roof arch. These centers 
are set up midway between the fan-like strutting frames previ- 
ously described. They are usually built of square timbers. 
The tie beams are usually Q x ^ in., and the struts and posts 
4 X 4 in. timbers. Tlie reason for giving the larger sectional 




Fig. 



70. —Sketch Showing Roof Arch 
Center, Belgian Method. 



148 TUNNELING 

dimensions to the tie beams, contrary to the usual practice in 
constructing centers, is that it has to serve as a sill for distrib- 
uting the pressure to the foundation of unexcavated soil 
which supports the center. Sometimes a sub-sill is used to 
support the center upon the soil ; and in any case wedges are 
employed to carry it, which can be removed for the purpose of 
striking the center. After the arch is completed, the centers 
may be removed immediately, or may be left in position until 
the masonry has thoroughly set. In either case the leading 
center over which the arch masonry terminates temporarily is 
left in position until the next section of the arch is built. 

Masonry. — The masonry of the roof arch, which is the first 
part built, is of necessity begun at the springing lines, and the 
first course rests on short lengths of heavy planks. These 
planks, besides giving an even surface upon which to begin the 
masonry, are essential in furnishing a bearing to the struts 
inserted to support the arch while the earth below them, part 
No. 5, Fig. 68, is being excavated. As the arch masonry 
progresses from the springing lines upward, the radial posts 
of the strutting are removed, and replaced by short struts rest- 
ing on the lagging of the centers, which support the crown 
bars or longitudinals until the masonry is in place, when they 
and the poling-boards are removed, and the space between the 
arch masonry and walls of the excavation is filled with stone 
or well-rammed earth. 

Considering now the side wall masonry, it will be re- 
membered that in excavating the part No. 5, Fig. 68, of the 
section, frequent side trenches were excavated, and struts 
inserted to take the weight of the masonry. These struts are 
inserted on a batter, with their feet near the center of the 
tunnel floor, so that the side wall masonry may be carried up 
behind them to a height as near as possible to the springing 
lines of the arch. When this is done the struts are removed, 
and the space remaining between the top of the partly fin- 
ished side wall and the arch is filled in. This leaves the arch 



TUNNELS THROUGH SOFT GROUND 



U9 



supported by alternate lengths or pillars of unexcavated earth 
and completed side wall. The next step is to remove the 
remaining sections of earth between the sections of side wall, 
and fill in the space with masonry. 
Fig. 71 is a cross-section, showing 
the masonry completed for one-half 
and the inclined props in position 
for the other half; and Fig. 72 is 
a longitudinal section showing the 
pillars of unexcavated earth be- 
tween the consecutive sets of in- 
clined struts and several other 
details of the lining, strutting, and 
excavating work. 

The invert masonry is built after 
the side walls are completed. This 
is regarded as a defect of this method of tunneling, since the 
lateral pressures may squeeze the side walls together and dis- 
tort the arch before the invert is in place to brace them apart. 




Fig. 71. — Sketcli Showing Method of 
Underpining Koof Arch with the 
Side Wall Masonry, 




To prevent as much as possible 
the distortion of the arch after 
the centers are removed, it is 
considered good practice to 
shore the masonry with hori- 
zontal beams having their ends 
abutting against plank, as shown by Fig. 71. These hori- 
zontal beams should be placed at close intervals, and be 
supported at intermediate points by vertical posts, as shown 



Fig. 72.— Longitudinal Section Showing 
Construction by the Belgian Method. 



150 TUNNELING 

by the illustration. Since the roof arch rests for some time 
supported directly by the unexcavated earth below, settle- 
ment is liable, particularly in working through soft ground. 
This fact may not be very important so long as the settle- 
ment is uniform, and is not enough to encroach on the space 
necessary for the safe passage of tra^'el. To prevent the 
latter possibility the centers are placed from 9 ins. to 15 ins. 
higher than their true positions, depending upon the nature of 
the soil, so that considerable settlement is possible without any 
danger of the necessary cross-section being infringed upon. 
In conclusion it may be noted that the lining may be con- 
structed in a series of consecutive rings, or as a single cylin- 
drical mass. 

Hauling. — Since in this method of tunneling the upper part 
of the section is excavated and lined before the excavation of 
the lower part is begun, the upper portion is always more ad- 
vanced than the lower. To carry away the earth excavated at 
the front, therefore, an elevation has to be surmounted; and 
this is usually done by constructing an inclined plane rising 
from the floor of the tunnel to the floor of the heading, as shown 
by Fig. 66. This inclined plane has, of course, to be moved ahead 
as the work advances, and to permit of this movement with as 
little interruption of the other work as possible, two planes are 
employed. One is erected at the right-hand side of the section, 
and serves to carry the traffic while the left-hand side of the 
lower section is being removed some distance ahead and the 
other plane is being erected. The inclination given to these 
planes depends upon the size of the loads to be hauled, but they 
should always have as shght a grade as practicable. Narrow- 
gauge tracks are laid on these planes and along the floor of the 
upper part of the section passing through the center opening 
mentioned before as being left in the centers and strutting. 

In excavating the top center heading there is, of course, an- 
other rise to its floor from the floor of the upper part of the 
section. Where, as is usually the case in soft soils, this top 



TUNNELS THliOUGH SOFT GROUND 151 

heading is not driven very far in advance, the earth from tiie 
front is usually conveyed to the rear in wheelbarrows, and 
dumped into the cars standing on the tracks below. In firm 
soils, where the heading is driven too far in advance to make 
this method of conveyance adequate, tracks are also laid on 
the floor of the heading, and an inclined plane is built connect- 
ing it with the tracks on the next level below. In place of 
these inclined planes, and also in place of those between the floor 
of the tunnel and the level above, some form of hoisting device 
is sometimes employed to lift the cars from one level to the 
other. There are some advantages to this method in point of 
economy, but the hoisting-machines are not easily worked in 
the darkness, and accidents are likely to occur. 

In the advanced top heading and in the upper part of the 
section narrow-gauge tracks are necessarily employed, and these 
may be continued along the floor of the finished section, or the 
permanent broad-gauge railway tracks may be laid as fast as 
the full section is completed. In the former case the perma- 
nent tracks are not laid until the entire tunnel is practically 
completed ; and in the latter case, unless a third rail is laid, the 
loads have to be transshipped from the broad- to the narrow- 
gauge tracks or vice versa. It is the more general practice to 
use a third rail rather than to transship every load. 

Modifications. — Considering the extent to which the Belgian 
method of tunneling has been employed, it is not surprising 
that many modifications of the standard mode of procedure 
have been developed. The modification which differs most 
from the standard form is, perhaps, that adopted in excavating 
the Roosebeck tunnel in Germany. This method preserves the 
principal characteristic of the Belgian method, which is the 
construction of the upper part of the section first ; but instead 
of building the side walls from the bottom upward, they are 
built in small sections from the top downward. The excavation 
begins by driving the center top heading No. 1, Fig. 73, whose 
floor is at the level of the springing lines of the roof arch, and 



152 



TUNNELING 



then the two side parts No. 2 are excavated, opening up the 
entire upper portion of the section in which the roof arch is 
built, as in the regular Belgian method. The next step is to 
excavate part No. 3, shoring up the arch 
at frequent intervals. Between these sets 
of shoring the side walls are built, resting 
on planks on the floor of part No. 3, and 
then the sets of shores are removed and re- 
placed by masonry. Next part No. 4 is 
excavated, shored, and filled with masonry 
as was part No. 3. In exactly the same 
way parts 5, 6, 7, and 8 are constructed 
in the order numbered. To prevent the 
distortion of the arch during the side-wall 
braced by horizontal struts, as radicated 



/ 2 


\ 


Z \ 


4. 


3 


6 


5 


8 


7 



Fig. 73. —Diagram Show- 
ing Sequence of Excava- 
tion in Modified Belgian 
Method. 



construction it is 
above in Fig. 71. 

Advantages. — The advantages of the Belgian method of 
tunneling may be summarized as follows : (1) The excavation 
progresses simultaneously at several points without the differ- 
ent gangs of excavators interfering with each other, thus secur- 
ing rapidity and efficiency of work ; (2) the excavation is done 
by driving a number of drifts or parts of small section, which 
are immediately strutted, thus causing the minimum disturb- 
ance of the surrounding material ; (3) the roof of the tunnel, 
which is the part of the lining exposed to the greatest pressures, 
is built first. 

Disadvantages. — The disadvantages of the Belgian method 
of tunneling may be summarized as follows : (1) The roof arch 
which rests at first on compressible soil is liable to sink ; (2) 
before the invert is built there is danger of the arch and side 
walls being distorted or sliding under the lateral pressures ; (3) 
the masonry of the side walls has to be underpinned to the arch 
masonry. 

Accidents and Repairs.— One of the most frequent accidents 
in the Belgian method of tunneling is the sinking of the roof 



TUNNELS THROUGH SOFT GliOUND 



153 



arch owing to its unstable foundation on the unexcavated soil 
of the lower portion of the section. The amount of settlement 
may vary from a few inches in firm soil to over 2 ft. in loose 
soils. To counteract the effect of this settlement it is the gene- 
ral practice to build the arch some inches higher than its nor- 
mal position. When the settlement is great enough to infringe 
seriously upon the tunnel section, repairs have to be made ; and 
the only way of accomphshing them is to demolish the arch and 
rebuild it from the side walls. It is usually considered best not 
to demohsh the arch until the invert has been placed, so that 

no further disturbance is hkely to occur 
once the lining is completed anew. 

The rotation of the arch about its 
keystone, or the opening of the arch at 
the crown, by the squeezing inward of 
the haunches by the lateral pressures, 
is another characteristic accident. Fig. 
74 shows the nature of the distortion 
produced ; the segments of the arch 
move toward each other by revolving 
on the intradosal edges of the keystone, 
which are broken away and crushed together with the operation, 
while the extradosal <edges are opened. It is to prevent this 
occurrence that the horizontal struts shown in Fig. 71 are em- 
ployed. The manner of repairing this accident differs, depend- 
ing upon the extent of the injury. When the intradosal edges 
of the keystone are but slightly crushed, the repairing is done 
as directed by Fig. 75. When the keystone is completely 
crushed, however, the indications are that the material of the 
keystone, usually brick, is not strong enough to resist the 
pressures coming upon it, and it is advisable to substitute a 
stronger material in the repairs, and a stone keystone is con- 
structed as shown by Fig. 75. The middle stone of this key- 
stone extends through the depth of the arch ring, and the two 
side stones only half-way through, their purpose being merely 




Fig. 74. — Sketch Showing 
Failure of Roof Arch by 
Opening at Crown. 



154 



TUNNELjj<G 



to resist the crushing forces which are greatest at the intrados. 
Sometimes, when the pressures are unsymmetrical, the arch 
ring breaks at tlie haunches as well as the crown, as shown by 




Fig. 75. — Sketches Showing Methods of Repairing Roof Arch Failures. 

Fig. 75, which also indicates the mode of repairing. This 
consists in demolishing the original arch, and rebuilding it 
with stone voussoirs inserted in place of the brick in which the 
rupture occurred. 



GERMAN METHOD 



155 



CHAPTER XIII. 

THE GERMAN METHOD — EXCAVATING TUN- 

NELS THROUGH SOFT GROUND (Continued); 

BALTIMORE BELT LINE TUNNEL. 



The German method of tunneling was first used in 1803 
in constructing the St. Quentin Canal. In 1837 the Konigs- 
dorf tunnel of the Cologne and Aix la Chapelle R.R. was 
excavated by the same method. The success of the method in 
these two difficult pieces of soft-ground tunnehng led to its 
extensive adoption throughout Germany, and for this reason 
it gradually came to be designated as the German method. 
Briefly explained the method consists in excavating first an 
annular gallery in which the side walls and roof arch are built 
complete before taking out the center core and building the 
invert. 

Excavation. — The excavation of tunnels by the German 
method is begun either by driving two bottom side drifts or 
by driving a center top heading. Fig. 76 shows the mode of 



/ "^ 


3 




4 \ 


2 


5 


2 






1 




I 



/ 5 


4 


5 \ 


3 


6 


3 


2 


2 


' 


I 



FiQ. 76. — Diagrams Showing Sequence of Excavation in German Method 
of Tunneling. 

procedure when bottom side drifts are used to start the work. 
The two side drifts No. 1 are made from 7 ft. to 8 ft. wide, 
and about one-third the total height of the full section ; the 



156 



TUNNELING 



width of each heading has to be sufficient for the construction 
of the masonry and strutting, and for the passage of narrow 
spoil cars alongside them. These drifts are increased in height 
to the springing line of the arch by taking out the two drifts 
No. 2. Next the top center heading No. 3 is driven, and 
finally the two haunch headings No. 4 are excavated. The 
center core No. 5 is utilized to support the strutting until 
the side walls and roof arch are completed, when it is broken 
down and removed. In case of very loose material, where the 
first side drifts cannot be carried as high as one-third the 
height of the section, it is the common practice to make them 
about one-fourth the height, and to take out the side portions 
of the annular gallery in three parts, as 
shown by Fig. 76. 

The top center heading plan of com- 
mencing the excavation is usually em- 
ployed in firm materials or when a vein 
of water is encountered in the upper part 
of the section. In the latter contingency 
a small bottom drift A, Fig. 77, is first 
driven to serve as a drain ; but in any 
case the excavation proper of the tunnel 
consists in first driving the center top 
heading No. 1, and then by working both 
ways along the profile parts, Nos. 2, 3, 4, and 5 are removed. 
Part No. 6 is left to support the strutting until the side walls 
and roof arch are built, when it is also excavated. 

Strutting. — When the excavation is begun by bottom side 
drifts these drifts are strutted by erecting vertical posts close 
against the sides of the drift and placing a cap-piece trans- 
versely across the roof of the drift. The side posts are 
usually supported by sills placed across the bottom of the drift. 
These frameworks of posts, cap, and sill are erected at short 
intervals, and the roof, and, if necessary, the sides of the drift 
between them, are sustained by means of longitudinal poling- 



^ 


• 


^ 


4 


6 


4- 


5 


J\ ^ 



FiG. 77.— Diagram Show- 
ing Sequence of Excava- 
tions in Water Bearing 
Material, German 
Method. 



GERMAN METHOD 



157 



boards extending from one frame to the next. The cap-pieces 
of the strutting for the bottom drifts serve as sills for the 
exactly similar strutting of the heading next above. To sup- 
port the additional weight, and to allow the construction of the 
side walls, the strutting of the bottom drifts is strengthened by 
inserting an intermediate post between the original side posts 
of each frame. These intermediate posts are not inserted at 
the center of the frames or bents, but close to the wall masonry 
line as shown by Fig. 78. This eccentric position of the post 





Fig. 78. — Sketch Showing Work of Ex- 
cavating and Timbering Drifts and 
Headings. 



Fig. 79. — Sketch Showing Method of 
Roof Strutting. 



avoids any interference with the hauling, and also allows the 
removal of the adjacent side post when the masonry is 
constructed. 

Two methods of strutting the soffit of the excavation are 
employed, one being a modification of the longitudinal system 
employed in the English method of tunneling described in a 
succeeding chaptsr, and the other a modification of the Belgian 
system previously described. Fig. 79 shows the method of 
employing the radial strutting of the Belgian system. At the 
beginning the center top heading is strutted with rectangular 
bents such as are employed for strutting the drifts. As this 
heading is enlarged by taking out the haunch sections, radial 
posts are inserted, as shown by Fig. 79, which also indicates 



158 



TUNNELING 



the method of strutting the side trenches when the excavation 
is carried downward from the center top heading instead of 
upward from bottom side drifts. 

Masonry. — Whatever plan of excavation or strutting is 
employed, the construction of the masonry lining in the German 
method of tunneling begins at the foundations of the side walls 
and is carried upward to the roof arch. The invert, if one is 
required, is built after the center core of earth is removed. 

Centering. — Tunnel centers are generally employed in the 
German method of tunneling, a common construction being 

shown by Fig. 80. It is essen- 
tially a queen-post truss, the tie 
beam of which rests on a transverse 
sill as shown by the illustration. 
The transverse sill is supported 
along its central portion by the 
unexcavated center core of earth, 
and at its ends either directly on 
the vertical posts or on longitudi- 
nal beams resting on these posts. 
The diagonal members of the 
queen-post truss form the bottom 
chords of small king-post trusses 
which are employed to build out the exterior member of the 
center to a closer approximation to the curve of the arch. 

Hauling. — When the bottom side drift plan of excavation 
is employed, the spoil from the front of the drift is removed in 
narrow-gauge cars running on a track laid as close as practicable 
to the center core. These same cars are also employed to take 
the spoil from the drifts above, through holes left in the ceiling 
strutting of the bottom drifts. The spoil from the soffit sec- 
tions may be removed by the same car lines used in excavating 
the drifts, or a narrow-gauge track may be laid on the top of the 
center core for this special purpose. In the latter case the soffit 
tracks are usually connected by means of inclined planes with 




Fig. 80. — Sketch Showing Roof Arch 
Centers and Arch Construction. 



GEBMAN METHOD 159 

the tracks on the bottoms of the side drifts. Generally, how- 
ever, the separate soffit car line is not used unless the material 
is of such a firm character that the headings and drifts can be 
carried a great distance ahead of the masonry work. With the 
center top heading plan of beginning the excavation, the car 
track has, of course, to be laid on the top of the center core. 
The center core itself is removed by means of car tracks along 
the floor of the completed tunnel. 

Advantages and Disadvantages. — Like the Belgian method 
of tunneling, the German method has its advantages and dis- 
advantages. Since the excavation consists at first of a narrow 
annular gallery only, the equilibrium of the earth is not greatly 
disturbed, and the strutting does not need to be so heavy as in 
methods where the opening is much larger. The undisturbed 
center core also furnishes an excellent support for the strutting, 
and for the centers upon which the roof arches are built. 
Another important advantage of the method is that the con- 
struction of the masonry lining is begun logically at the bottom, 
and progresses upward, and a more homogeneous and stable 
construction is possible. The great disadvantage of the method 
is the small space in which the hauling has to be done. The 
spoil cars practically fill the narrow drifts in passing to and from 
the front, and interfere greatly with the work of the carpenters 
and masons. Another objection to the method is that the 
invert is the very last portion of the lining to be built. This 
may not be a serious objection in reasonably compact and stable 
materials, but in very loose soils there is always the danger of 
the side walls being squeezed together before the invert masonry 
is in position to hold them apart. Altogether the difficulties 
are of a character which tend to increase the expense of the 
method, and this is the reason why to-day it is seldom used 
even in the country where it was first developed, and for some 
time extensively employed. For repairing accidents, such as 
the caving in of completed tunnels, the German method of tun- 
neling is frequently used, because of the ease with which the 



160 TUNNELING 

timbering is accomplished. In such cases the cost of the method 
used cuts a small figure, so long as it is safe and expeditious. 

BALTIMORE BELT LINE TUNNEL 

In the last few years a modification of the German method 
was used in this country for the construction of several railroad 
tunnels. The modification consists in excavating the two-side 
drifts up to the springing line of the arch of the proposed tunnel. 
Then a central heading, which is afterward enlarged to the whole 
section of the tunnel, is excavated close to the crown. At the 
same time the masonry is constructed from the foundation up 
in the side drifts. From the floor of the upper section already 
excavated and strutted, the top of the masonry of the drifts is 
reached by means of small side cuts; thus the lining is made 
continuous up to the keystone. The central nucleus or bench 
is removed after the tunnel has been lined. 

The most important tunnel excavated by this method was 
the Baltimore Belt Line tunnel described as follows : 

The Baltimore Belt Ry. Co. was organized in 1890 by officials 
of the Baltimore & Ohio, and Western Maryland railways, 
and Baltimore Capitalists, to build 7 miles of double track 
railway, mostly within the city limits of Baltimore. This rail- 
way was partly open cut and embankment, and partly tunnel, 
and its object was to afford the companies named facilities for 
reaching the center of the city with their passengers and freight. 
To carry out the work the Maryland Construction Co. was 
organized by the parties interested, and in September, 1890, this 
company let the contract for construction to Ryan & McDon- 
ald of Baltimore, Md. The chief difficulties of the work cen- 
tered in the construction of the Howard-street tunnel, 8350 ft. 
long, running underneath the principal business section of 
the city. 

Material Penetrated. — The soil penetrated by the tunnel was 
of almost all kinds and consistencies, but was chiefly sand of 
varying degrees of fineness penetrated by seams of loam, clay, 



GERMAN METHOD 161 

and gravel. Some of the clay was so hard and tough that 
it could not be removed except by blasting. Rock was also 
found in a few places. For the most part, however, the work 
was through soft ground, furnishing more or less water, which 
necessitated unusual precautions to avoid the setthng of the 
street, and consequent damage to the buildings along the line. 
A large quantity of water was encountered. Generally this 
water could be removed by drainage and pumps, and the earth 
be prevented from washing in by packing the space between the 
timbering with hay or other materials. At points where the 
inflow was greatest, and the earth was washed in despite the 
hay packing, the method was adopted of driving 6-in. perfo- 
rated pipes into the sides of the excavation, and forcing cement 
grout through them into the soil to solidify it. These pipes 
penetrated the ground about 10 ft., and the method proved 
very efficient in preventing the inflow of water. 

Excavation. — The excavation was carried out according to 
the German method of tunneling. Bottom side drifts were 
first driven, and then heightened to the springing line of the 
roof arch. Next a center top heading was driven, and the 
haunch sections taken out. The object of beginning the exca- 
vations by bottom side drifts, was to drain the soil of the upper 
part of the section. The center core was removed after the 
side walls and roof arch were completed, its removal being kept 
from 50 ft. to 75 ft. to the rear of the advanced heading. The 
dimensions of the side drifts proper were about 8 X 8 ft., but 
they were often carried down much below the floor level to secure 
a soHd foundation bed for the side walls. 

Strutting. — The side drifts were strutted by means of frames 
composed of two batter posts resting on boards, and having a 
cap-piece extending transversely across the roof of the drift. 
These frames were spaced about 4 ft. apart. The excavation 
was advanced in the usual way by driving poling-boards at the 
top and sides, with a shght outward and upward inclination, 
so that the next frame could be easily inserted leaving space 



162 



TUNNELIKG 



enough between it and the sheeting to permit the next set of 
poling-boards to be inserted. These pohng-boards were driven 
as close together as practicable so as to prevent as much as 
possible the inflow of water and earth. 

The center top heading was strutted in the same manner as 
were the side drifts. The arrangement of the strutting em- 







Fig. 81. — Sketch Showing Method of Excavating and Strutting Baltimore Belt 
Line Tunnel. 

ployed in enlarging the center top heading is shown clearly by 
Fig. 81, which also shows the manner of strutting the side drifts 
and face of the excavation, and of building the masonry. 

Centers. — Both wood and iron centers were employed in 
building the roof arch. The timber centering was constructed 
of square timbers, as shown by Fig. 82. This construction of 
the iron centers is shown by Fig. 83. Each of the iron centers 
consisted of two 6 X 6 in. angles butted together, and bent into 
the form of an arch rib. Six of these ribs were set up 4 ft. 



GERMAN METHOD 



163 



apart. They were made of two half ribs butted together at the 
crown, and were held erect and the proper distance apart by 
spacing rods. The rearmost rib was held fast to the completed 
arch masonry, and in turn supported the forward ribs while the 
lagging was being placed. 

Masonry. — The side walls of the lining were built first in 




Fig. 82. — Roof Arch Construction with Timber Centers, Baltimore Belt Line Tunnel. 



the bottom side drifts, as shown by Fig. 81. They were gen- 
erally placed on a foundation of concrete, from 1 ft. to 2 ft. 
thick. As a rule the side walls were not built more than 20 
ft. in advance of the arch, but occasionally this distance was 
increased to as much as 90 ft. The roof arch consisted ordina- 
rily of five rings of brick, but at some places in especially un- 
stable soil eight rings of brick were employed. The arch was 
built in concentric sections about 18 ft. in length. All the 



164 



TUNNELING 



timber of the strutting above the arch and outside of the side 
walls was left in place, and the voids were filled with rubble 
masonry laid in cement mortar. It required about 125 mason 
hours to build an 18-ft. arch section. Figs. 82 and 83 show 
various details of the masonry arch work. 

Owing to the very unstable character of the soil, consider- 
able difficulty was experienced in building the masonry invert. 
The process adopted was as follows: Two parallel 12 X 12 in. 
timbers were first placed transversely across the tunnel, abutting 




Fig. 83. — Roof Arch Construction with Iron Centers, Baltimore Belt Line Tunnel. 



against longitudinal timbers or wedges resting against the side 
walls. Short sheet piles were then driven into the tunnel bot- 
tom outside of these timbers, forming an inclosure similar to 
a cofferdam, from which the earth could be excavated with- 
out disturbing the surrounding ground. The earth being 
excavated, a layer of concrete 8 ins. thick was placed, and the 
brick masonry invert constructed on it. In less stable ground 
each of the above described cofferdams was subdivided by 
transverse timbers and sheet piling into three smaller coffer- 
dams. Here the masonry of the middle section was first con- 



GERMAN METHOD 165 

structed, and then the side sections built. ^Vhere the ground 
was worst, still more care was necessary, and the bottom had 
to be covered with a sheeting of li-in. plank held down by 
struts abutting against the large transverse timbers. The in- 
vert masonry was constructed on this sheeting. Refuge niches 
9 ft. high, 3 ft. wide, and 15 ins. deep were built in the side 
walls. 

Accidents. — In this tunnel, owing to the quick striking of 
the centers, it was found that the masoniy lining flattened at 
the crown and bulged at the sides. This was attributed to the 
insufficient time allowed for the mortar to set in the rubble 
filling. Earth packing was tried, but gave still worse results. 
Finally dry rubble filling was adopted, with satisfactory results. 
There was necessarily some sinking of the surface. This re- 
sulted partly from the necessity of changing and removing of 
the timbers, and from the compression and springing of the 
timbers under the great pressures. The crown of the arch also 
settled from 2 ins. to 6 ins., due to the compression of the mortar 
in the joints. The maximum sinking of the surface of the 
street over the tunnel was about 18 ins.; it usually ran from 
1 to 12 ins. Some damage was done to the water and gas mains. 
This damage was not usually serious, but it of course necessitated 
immediate repairs, and in some instances it was found best to 
reconstruct the mains for some distance. At one point along 
the tunnel where very treacherous material was found, the 
surface settlement caused the collapse of an adjacent building, 
and necessitated its reconstruction. 



166 TUNNELING 



CHAPTER XIV. 

THE FULL SECTION METHOD OF TUNNELING 

ENGLISH METHOD; AMERICAN METHOD; 

AUSTRIAN METHOD. 



ENGLISH METHOD. 

The English method of tunneUng through soft ground, as 
its name implies, originated in England, where, owing to the 
general prevalence of comparatively firm chalks, clays, shales, 
and sandstones, it has gained unusual popularity. The dis- 
tinctive characteristics of the method are the excavation of the 
full section of the tunnel at once, the use of longitudinal strut- 
ting, and the alternate execution of the masonry work and 
excavation. In America the method is generally designated as 
the longitudinal bar method, owing to the mode of strutting, 
which has gained particular favor in America, and is commonly 
employed here even when the mode of excavation is distinc- 
tively German or Belgian in other respects. 

Excavation. — Although, as stated above, the distinctive 
characteristic of the English method is the excavation of the 
full section at once, the digging is usually started by driving 
a small heading or drii't to locate and establish the axis of the 
tunnel, and to facilitate drainage in wet ground. These ad- 
vance galleries may be driven either in the upper or in the 
lower part of the section, as the local conditions and choice 
of the engineer dictate. Whether the advance gallery is located 
at the top or at the bottom of the section makes no difference in 
the mode of enlarging the profile. This work always begins 
at the upper part of the section. A center top heading is 
driven and strutted by erecting posts carrying longitudinal bars 
supporting transverse poling-boards. This heading is imme- 




THE FULL SECTION METHOD 167 

diately widened by digging away the earth at each side, and by 
strutting the opening by temporary posts resting on blocking, 
and carrying longitudinal bars supporting poling-boards. This 
process of widening is continued in this manner until the full 
roof section, No. 1, Fig. 84, is opened, when a heavy transverse 
sill is laid, and permanent struts are 
erected from it to the longitudinal bars, 
the temporary posts and blocking being 
removed. The excavation of part No. 2 
then begins by opening a center trench 
and widening it on each side, temporary 
posts being erected to support the sill 
above. As soon as part No. 2 is fully ex- 
cavated, a second transverse sill is placed ^'.^- s*. - Diagram Sho.^^- 

' ■•■ mg Sequence of Excava- 

below the first, and struts are placed tion in English ivretiiod 
between them. The excavation of part ^ ^^^^ ^"^' 
No. 3 is carried out in exactly the same manner as was part 
No, 2. The lengths of the various sections, Nos. 1, 2, and 3, 
generally run from 12 ft. to 20 ft., depending upon the 
character of the soil. 

Strutting The strutting in the English method of tunnel- 
ing consists of a transverse framework set close to the face of 
the excavation, which supports one end of the longitudinal 
crown bars, the other ends of which rest on the completed 
lining. The transverse framework is composed of three hori- 
zontal sills arranged and supported as shown by Fig. 85. The 
bottom sill A is carried by vertical posts resting on blocking on 
the floor of the excavation. From the bottom sill vertical 
struts rise to support the middle sill B. The top sill, or miners' 
sill (7, is carried by vertical posts or struts rising from the 
middle sill B. The vertical struts are usually round timbers 
from 6 ins. to 8 ins. in diameter ; and the sills are square tim- 
bers of sufficient section to carry the vertical loads, and gener- 
ally made up of two posts scarf -jointed and butted to permit 
them to be more easily handled. In firm soils the struts be- 



168 



TUNNELING 



tween the sills are all set vertically, but those at the extreme 
sides of the roof section are inclined. In loose soils, however, 
where the sides of the excavation must be shored, the V- 
bracing shown by Fig. 85 is employed between one or more 
pairs of sills as the conditions necessitate. The manner of 
holding the transverse framework upright is explained quite 
clearly by Fig. 85 ; inclined props extending from the com- 
pleted masonry to the sills of the framework being employed. 
Two props are used to each sill. Sometimes, in addition to the 




Fig. 85. — Sketches Showing Construction of Strutting, English Method. 



props shown, another nearly horizontal prop extends from the 
crown of the arch masonry to the middle piece of the strutting. 
Referring to Fig. 85, it will be observed that the longitudinal 
crown bars are above the extrados of the roof arch. When, 
therefore, the lining masonry has been completed close up to 
the transverse framework, the latter is removed, leaving the 
crown bars resting on the arch masonry ; and excavation, which 
has been stopped while the masonry was being laid, is continued 
for another 12 ft. to 20 ft., and the transverse framework is 
erected at the face, and braced or propped against the completed 
lining as shown by Fig. 85. The next step is to place the 



THE FULL SECTION METHOD 



169 



crown bars, and this is done by pulling them ahead from their 
original position over the masonry of the completed section of 
the roof arch. It will be understood that the crown bars are 
not pulled ahead their full length at one operation, but are 
advanced by successive short movements as the excavation 
progresses, their outer ends being supported by temporary 
posts until the transverse framework is built at the face of the 
excavation. 

Centers Two standard forms of centers are employed in 

the English method of tunneling, as shown by Figs. 86 and 87. 
Both consist of an outer portion, constructed much like a 
typical plank center, which is strengthened against distortion 
by an interior truss framework. The elemental members of 




Figs. 86 and 87.— Sketches of Typical Timber Roof-Arch Centers, English Method. 

this truss framework take the form of a queen-post truss, as is 
shown more particularly by Fig. 86. In Fig. 87 the queen- 
post truss construction is less easily distinguished, owing to 
the cutting of the bottom tie-beam and other modifications, but 
it can still be observed. The possibility of cutting the tie-beam 
as shown in Fig. 87, without danger, is due to the fact that 
the lateral pressures on the haunches of the center counteract 
the tendency of the center to flatten under load, which is 
usually counteracted by the tie-beam alone. The object of 
cutting the tie-beam is to afford room for the props running 
from the completed masonry to the transverse framework of 
the strutting as shown by Fig. 85. 

Generally four or five centers are used for each length of 
arch built. They are set up so that the tie-beams rest on 



170 TUNNELING 

double opposite wedges carried by a transverse beam below. 
This transverse beam in turn i-ests on another transverse beam 
which is supported by posts carried on blocking on the invert 
masonry. It is usually made with a butted joint at the middle 
to permit its removal, since it is so long that the masonry has 
to be built around its extreme ends. The lagging is of the 
usual form, and rests on the exterior edges of the curved upper 
member of the centers. 

Masonry. — In the English method of tunneling, the masonry 
begins with the construction of the invert, and proceeds to the 
crown of the arch. The lining is built in lengths, or successive 
rings, corresponding to the length of excavation, which, as pre- 
viously stated, is from 12 ft. to 20 ft. Each ring or length of 
lining terminates close to the transverse strutting frame erected 
at the face of the excavation. Work is first begun on the 
invert at the point where the preceding ring of masonry ends, 
and is continued to the transverse strutting frame at the front 
of the excavation. As fast as the invert is completed, work is 
begun on the side walls. In very loose soils the longitudinal 
bars supporting the sides of the excavation are removed after 
the side walls are built; but in firmer soils they may be taken 
out one by one just ahead of the masonry, or in very firm soils 
it may be possible to remove them entirely before beginning 
the side walls. In all cases it is necessary to fill the space 
between the masonry and the walls of the excavation with rip- 
rap or earth. To build the roof arch the centers are first 
erected as described above, and the crown bars are removed as 
previously described by pulling them ahead after the arch ring 
is completed. As with the side walls, the vacant space be- 
tween the arch ring and the roof of the excavation must 
be filled in. Usually earth or small stones are used for filling ; 
but in very loose soils it is sometimes the practice not to 
remove the poling-boards, but to support them by short brick 
pillars resting on the arch ring and then to fill around these 
pillars. 



THE FULL SECTION METHOD 171 

Hauling. — To haul away the material and take in supplies, 
tracks are laid on the invert masonry. Generally the perma- 
nent tracks are laid as fast as the lining is completed. A short 
section of temporary track is used to extend this permanent 
track close to the work of the advanced drift. 

Advantages and Disadvantages. — The great advantage of the 
English method of tunneling is that the masonry lining is 
built in one piece from the foundations to the crown, making 
possible a strong, homogeneous construction. It also pos- 
sesses a decided advantage because of the simple methods of 
hauling which are possible : there being no differences of level 
to surmount, no hoisting of cars nor trans-shipments* of loads 
are necessary. The chief disadvantage of the method is that 
the excavators and masons work alternately, thus making the 
progress of the work slower perhaps than in any other method 
of tunnehng commonly employed under similar conditions. 
This disadvantage is overcome to a considerable extent when 
the tunnel is excavated by shafts, and the work at the different 
headings is so arranged that the masons or excavators when 
freed from duty at one heading may be transferred to another 
where excavation or lining is to be done as the case may be. 
Another disadvantage of the English method arises from the 
excavation of the full section at once, which in unstable soils 
necessitates strong and careful strutting, and increases the 
danger of. caving. The fact also that the arch ring has to 
carry the weight of the crown bars, and their loading at one 
end while the masonry is green, increases the chances of the 
arch being distorted. 

Conclusion. — The English method of tunneling in its entirety 
is confined in actual practice pretty closely to the country from 
which it receives its name. A possible extension of its use 
more generally is considered by many as likely to follow the 
development of a successful excavating machine for soft 
material. The space afforded by the opening of the full sec- 
tion at once, especially adapts the method to the use of exca- 



172 TUNNELING 

vators like, for example, the endless chain bucket excavator 
used on the Central London Ry., and illustrated in Fig. 12. 
The method also furnishes an excellent opportunity for electric 
hauling and lighting during construction. 

The English method of tunneling has been used in building 
the Hoosac, Musconetcong, Allegheny, Baltimore and Potomac, 
and other tunnels in America. The names of the European 
tunnels built by this method are too numerous to mention here. 

AMERICAN METHOD. 

In this country tunnels through loose soils are excavated 
according to the " Crown Bar " or American Method. This 
consists in opening the whole section of 
the tunnel before the construction of the 
lining as in the English Method. It differs 
from the English method, however, in that 
many timber structures are erected for the 
support of the roof, and that the excava- 
tion and construction of the lining are far 
Fig. 88. -Sequence of Ex- apart, SO allowiug the mincrs and the masons 
cavation in the Ameri- ^q ^qj.]^ contiuuously and without iutcrfer- 

can Method. 

ing with each other. 
Excavation. — The diagram in Fig. 88 shows the sequence of 
excavation. The work begins by driving a central heading 
usually 7 X 8 ft., strutted by means of vertical 
or batter posts and cap-piece. Fig. 89,* the props r^^m^^^zVifsgiv 
resting on foot blocks. Between the cap-pieces 
of the consecutive frames are placed planks 
driven upward at a slightly inclined angle. 
After the heading has been excavated and fig. 89. - strutting 

. . , the Heading in the 

strutted, the floor is lowered by removing the American Method. 
part marked 2 in the figure. The two batter 
posts supporting the cap-piece are now substituted by two 
longer ones resting on the floor of part 2 and abutting against 

* Figs. 89 to 91 are taken from a paper by S. W. Hopkins in Harvard Engineering Journal, 
April, '03, on the Fort George tunnel. 





THE FULL SECTION METHOD 



173 



longitudinal beams which are inserted underneath the cap-pieces. 
These longitudinal beams are called crown bars. The new 
batter posts are resting either on foot blocks or sills according 
to the quality of soil and they are strongly wedged to the crown 
bars. On each side of these crown bars are inserted poling- 
boards or planks close to each other, which are driven down- 
w^ard. The part marked 3 in the figure is removed by enlarging 
the cut 1 X 2 on both sides. The plank, inserted above the 
crown bar, is driven in either preceding or following the excava- 
tion and another crown bar is inserted at the end of this plank. 
This second crown bar is supported by a prop whose other end 
abuts against the foot of the rafter strutting the heading. Be- 
tween this crown bar and the roof of the excavation, other 
planks are placed transversally to the axis of the tunnel and 
are driven in until they are supported by a new crown bar, etc. 
The various props supporting the crown bars are placed radially 
or in a fan-like manner, similar 
to the characteristic arrangement 
of the timbering in the Belgian 
method. Bracers to strengthen 
the timbering and the roof of the 
excavation are inserted longitudi- 
nally between the various posts 
and transversally between the 
crown bars. Fig. 90. As a rule, 

only three or four of these radial structures are temporarily 

erected. A trench is excavated at 
the side of the part marked 3 in the 
figure to receive the wall plate which 
is a heavy timber laid on the floor 
parallel to the longitudinal axis of 
the tunnel. On the wall plates are 
erected the arched timber sets com- 
posed of five or seven segments of 
hewn timbers so as to form a polygonal frame which is wedged 




Fig. 90. — Temporary Timbering of the 
Roof in the American Method. 




Fig. 



. Section E-F. 
91. — Showing Crown Bars Sup- 
ported by Segmental Arches. 



174 



TUNNELING 



to the crown bars and which will support the arch of the roof. 
After one of these segmental timber sets is erected the tempo- 
rary radial structure is removed and the upper section of the 
tunnel is cleared of any obstruction as the pressures are trans- 
ferred to the wall plates, Fig. 91. The bench marked 4 in the 
figure is taken away and the vertical props inserted under the 
wall plates, Fig. 92. 




Section 6- ^ 



Fig. 92. — Transversal and Longitudinal Section of a Tunnel Excavated and Strutted 
According to the American Method. 



Strutting^. — The longitudinal strutting is used in connection 
with the American method of tunneling. In fact, the strutting 
consists of a series of longitudinal bars supporting planks laid 
transversally to the axis of the tunnel and abutting against the 
roof of the excavation. These crown bars during the excava- 
tions and immediately after are temporarily supported by radial 
timbers forming almost a fan-like structure, but this is soon 
substituted by a permanent one composed of a polygonal timber 
frame of five or seven segments which are cut to dimensions. 
The batter posts of the heading, the radial posts of the temporary^ 
timber structure and the crown bars are all round timbers from 
10 to 12 ins. in diameter. All the other timbers are square 
edged, the usual dimensions being 10 X 10 ins. or 12 X 12 ins. 
with the exception of the wall plates which are 14 X 14 ins. 
The dimensions of the various members of the strutting and the 
distance apart of the different frames vary with the quality of 



THE FULL SECTION METHOD 175 

the soil. For instance, in ordinary loose soils the frames are 
placed between 4 to 6 ft., but in very soft soils they are erected 
only 3 or 3^ ft. apart. 

Chiefly in the southwest, in tunnels excavated according to 
the American method, the timbering has been left as regular 
lining and it was only after many years when this temporary 
structure had decayed or was burned down, that the tunnels 
were lined with masonry. But in many instances the whole 
timber structure was left in place even when the tunnel 
was lined with masonry immediately after the excavation had 
been made. This was usually done when the tunnel was lined 
with concrete masonr}^ In such a case the timbering was left 
to support the pressures of the roof while the concrete was 
plastic and before it hardened. 

Centers. — In the American method the whole section of the 
tunnel is open before the construction of the Hning, thus the 
masonry can be built from the foundations up. The centers are 
designed so as to support only the weight of the masonry during 
its construction and not the pressures of the tunnel as in the 
other methods and consequently they are of light construction. 
The centers described in the Murray Hill tunnel, page 127, may 
be advantageously used in building the concrete lining in tunnels 
through loose soils excavated by the American method. 

Hauling. — The excavation of the heading and the upper 
section of the tunnel is usually far ahead of the bench, conse- 
quently the hauHng of both the debris and the building materials 
is made at two different levels, viz., on the bench and on the 
floor of the tunnel. When the face of the heading and the ex- 
cavation of the bench are not more than 50 ft. apart, the 
hauling can be conveniently done on the tunnel floor, while 
the materials and debris on the upper section of the tunnel are 
hauled by wheelbarrows or light cars propelled by handpower. 
For a greater distance, however, it is more convenient to use 
light cars running on narrow-gauge tracks all through the tunnel. 
In this case the tracks on the tunnel floor and on top of the 



176 TUNNELING 

bench are connected by means of an inclined platform where 
the cars may ascend and descend without interfering with the 
excavation of the bench. Here, as a rule, tunnels have been 
excavated in soils considered good, generally through rock, while 
loose soils have been encountered only in small sections. The 
same method of excavation for whatever material is encountered 
is certainly very convenient, as it affords a great regularity in 
the work; hence its extensive use. A great disadvantage of this 
method is the double strutting, viz., the polygonal and the 
longitudinal strutting succeeding each other, whereas one of 
them could be easily spared. Another defect is that it re- 
quires a larger amount of excavation, in case the strutting, 
is left in place. 

AUSTRIAN METHOD. 

The Austrian full-section method of tunneling through soft 
ground was first used in constructing the Oberau tunnel on the 
Leipsic and Dresden R.R., in Austria in 1837. It consists in 
excavating the full section and building up the lining masonry 
from the foundations as in the English, but with the impor- 
tant exception that the invert is built last instead of first in 
all cases except where the presence of very loose soil requires 
its construction first. A still more important difference in the 
two methods is that the excavation is carried out in smaller 
sections and is continuous in the Austrian method instead of 
alternating with the mason work as it does in the English 
method. 

Excavation. — The excavation in the Austrian method begins 
by driving the bottom center drift No. 1, Fig. 93, rising from 
the floor of the timnel section nearly to the height of the spring- 
ing lines of the roof arch. When this drift has been driven 
ahead a distance varying from 12 ft. to 20 ft. or sometimes more, 
the excavation of the center top heading No. 2 is driven for the 
same distance. The next operation is to remove part No. 3, 
thus forming a central passage the full depth of the tunnel section 



THE FULL SECTION METHOD 



177 



at the center. This trench is enlarged by removing parts Nos. 4, 
5, 6, 7, and 8 in the order named until the full section is opened. 
A modification of this plan of excavation is shown by Fig. 94 
which is used in firm soils. 



/< 


2 


>\ 


h 


3 


y] 


8 \ 


■ 


7 / 



f 


2 


^ 


3 


6 


! 


6 



Figs. 93 and 94. — Diagrams Showing Sequence of Excavation in Austrian Method of Tunneling. 



Strutting. — Each part of the section is strutted as fast as 
it is excavated. The center bottom drift first excavated is 
strutted by laying a transverse sill across the floor, raising 
two side posts from it, and capping them with a transverse 
timber having its ends projecting beyond the side posts and 
halved as shown by Fig. 95. The top center heading No. 2, 
which is next excavated, is strutted by means of two side posts 
resting on blocking and carrying a transverse cap as also shown 
by Fig. 95. Sometimes the side posts in the heading strutting- 
frames are also carried on a transverse sill as are those of the 
bottom drift. This construction is usually adopted in loose 
soils. When the sill is employed, the middle part. No. 3, is 
strutted by inserting side posts between the bottom of the top 
sill and the cap of the frame in the drift below. When, how- 
ever, the posts of the top heading frame f^.re carried on blocking, 
it is the practice to replace them with long posts rising from 
the cap of the bottom drift frame to the cap of the top heading 
frame. Further, when the intermediate sill is employed at the 
bottom level of the top heading it projects beyond the side 
posts and has its ends halved. 

After the completion of the center trench strutting the next 



178 



TUNNELING 



task is to strut parts Nos. 4 and 5. This is done by continu- 
ing the upper sill by means of a timber having one end halved 
to join with the projecting end of the sill in position. This 
extension timber is shown at a, Fig. 96. The next operation is 
to place the timber h, having one end resting on the cap-piece 





of the top heading frame and 
the other beveled and resting 
on the top of the sill a near 
the end. The timber h is laid 
tangent to the curve of the 
roof arch, and to support it 
against flexure the strut c is 
inserted as shown. To sup- 
port the thrust of this strut 
the additional post d is in- 
serted and the original bottom 
heading frame is reinforced as 
shown. The next step is to 
insert the strut e, and when 
this and the previous construction are duplicated on the oppo- 
site side of the tunnel section we have the strutting of the parts 
Nos. 1 to 5, inclusive; complete. Part No. 6 is then removed and 



Figs. 95 to 97. — Sketches Showing Construc- 
tion of Strutting, Austrian Method. 



THE FULL SECTION METHOD 



179 



strutted by extending the bottom drift cap-piece by a timber 
similar to timber a above, and then by inserting a side strut 
between the outer ends of these two timbers, as indicated by 
Fig. 97. As the final parts, Nos. 7 and 8, are removed, the in- 
clined prop a, Fig. 97, is inserted as shown. When the soil is 
loose some of the members of the framework are doubled and 
additional bracing is introduced as shown by Fig. 97. 

The frames just described are placed at intervals of about 
4 ft. along the excavation, and are braced apart by horizontal 
struts. Some of the longitudi- 
nal bearing beams, as at h, Fig. 
90, also extend through two or 
three frames, and help to tie 
them together. Finally, the 
longitudinal poling-boards ex- 
tending from one frame to the 
next along the walls of the ex- 
cavation serve to connect them 
together. The short transverse 
beam c. Fig. 90, located just 
above the floor of the invert, 
serves to carry the planking 
upon which the train car tracks 
are laid. Besides the timber 
strutting peculiar to the Aus- 
trian method, the Rziha iron strutting described in a pre- 
vious chapter is frequently used in tunneling by the Austrian 
process. 

Centers. — The two forms of centers used in the English 
method of tunneling are also used in the Austrian method. 
One of the methods of supporting these centers is shown by 
Fig. 98. The tie-beam of the center rests on longitudinal tim- 
bers carried by the strutting frames and intermediate props. 
In single-track tunnels it is the frequent practice also to carry 
the ends of the tie-beams in recesses left in the side wall 




Fig. 98. — Sketch Showing Manner of 
Constructing the Lining Masonry, 
Austrian Method. 



180 TUNNELING 

masonry, with intermediate props inserted to prevent flexure 
at the center. When the Rziha iron strutting is employed, it 
also serves for the centering upon which the arch mas.onry is 
built. 

Masonry. — In the Austrian system of tunneling, the lining 
is built from the foundations of the side walls upward to the 
crown of the roof arch in lengths in consecutive rings equal to 
the lengths of the consecutive openings of the full section, or 
from 12 ft. to 20 ft. long. Except in infrequent cases in very 
loose materials the invert is the last part of the masonry to be 
built, since to build it first requires the removal of the strutting 
which cannot easily or safely be accomplished until the side walls 
and roof arch are completed. As the side wall foundations are 
built, however, their interior faces are left inclined, as shown 
by Figs. -97 and 98, ready for the insertion of the invert, and 
are meanwhile kept from sliding inward by the insertion of 
blocking between them and the bottom of the strutting. Fig. 
98 shows the nature of this blocking, and also the manner in 
which the side wall and roof arch masonry is carried upward. 
Finally when the roof arch is keyed and the centers are struck, 
the strutting is taken down and the invert is built. 

Advantages and Disadvantages. — The principal advantages 
claimed for the Austrian method of tunneling are: (1) The 
excavation being conducted by driving a large number of con- 
secutive small galleries, which are immediately strutted, there 
is little disturbance of the surrounding material; (2) the polyg- 
onal type of strutting adopted is easily erected and of great 
strength against symmetrical pressures; (3) the masonry, being 
built from the foundations up, is a single homogeneous structure, 
and is thus better able to withstand dangerous pressures; (4) 
the excavation is so conducted that the masons and excavators 
do not interfere, and both can work at the same time. The 
disadvantages which the method possesses are: (1) The strutting 
while very strong under symmetrical pressures, either vertical 
or lateral, is distorted easily by unsymmetrical vertical or lateral 



THE FULL SECTION METHOD 181 

pressures, and by pressure in the direction of the axis of the 
tunnel; (2) the construction of the invert last exposes the side 
walls to the danger of being squeezed together, causing a rotation 
of the arch of the nature discussed in describing the Belgian 
method of tunneling. 



182 TUNNELING 



CHAPTER XV. 

SPECIAL TREACHEROUS GROUND METHOD; 
ITALIAN METHOD; QUICKSAND TUN- 
NELING; PILOT METHOD. 



ITALIAN METHOD. 

The Italian method of tunneling was first employed in con- 
structing the Cristina tunnel on the Foggia & Benevento R.R. 
in Italy. ' This tunnel penetrated a laminated clay of the most 
treacherous character, and after various other soft-ground 
methods of tunneling had been tried and had failed, Mr. Procke, 
the engineer, devised and used successfully the method which 
is now known as the Italian or Cristina method. The Itahan 
method is essentially a treacherous soil method. It consists in 
excavating the bottom half of the section by means of several 
successive drifts, and building the invert and side walls ; the 
space is then refilled and the upper half of the section is exca- 
vated, and the remainder of the side walls and the roof arch 
are built ; finally, the earth filling in the lower half of the 
section is re-excavated and the tunnel completed. The method 
is an expensive one, but it has proved remarkably successful in 
treacherous soils such as those of the Apennine Mountains, 
in which some of the most notable Italian tunnels are located. 
It is, moreover, a single-track tunnel method, since any soil 
which is so treacherous as to warrant its use is too treacherous 
to permit an opening to be excavated of sufficient size for a 
double- track railway, except by the use of shields. 

Excavation. — The plan of excavation in the Italian method 
is shown by the diagram Fig. 99. Work is begun by driving 



SPECIAL TREACHEROUS GROUND METHOD 



183 




Fig. 99, —Diagram Show- 
iug Sequence of Excava- 
tion in Italian Method of 
Tunneling. 



the center bottom heading No. 1, and this is widened by taking 
out parts No. 2. Finally part No. 3 is removed, and the lower 
half of the section is open. As soon as the invert and side 
wall masonry has been built in this excavation, parts No. 2 
are filled in again with earth. The exca- 
vation of the center top heading No. 4 is 
then begun, and is enlarged by removing 
the earth of part No. 5. The faces of this 
last part are inclined so as to reduce their 
tendency to slide, and to permit of a 
greater number of radial struts to be 
placed. Next, parts No. 6 are excavated, 
and when this is done the entire section, 
except for the thin strip No. 7, has been 
opened. At the ends of part No. 7 nar- 
row trenches are sunk to reach the tops of the side walls 
already constructed in the lower half of the section. The 
masonry is then completed for the upper half of the section, 
and part No. 7 and the filling in parts No. 2 are removed. 
The various drifts and headings and ^^ — ^^ 

the parts excavated to enlarge them /^ 

are seldom excavated more than from 
6 ft. to 10 ft. ahead of the lining. / 

Strutting. — The bottom center 
drift, which is first driven, is strutted 
by means of frames consisting of side 
posts resting on floor blocks and car- 
rying a cap-piece. Poling-boards are 
placed around the walls, stretching 
from one frame to the next. As 
soon as the invert is sufficiently completed to permit it, the 
side posts of the strutting frames are replaced by short struts 
resting on the invert masonry as shown by Fig. 100. To permit 
the old side posts to be removed and the new shorter ones to 
be inserted, the cap-piece of the frame is temporarily supported 




Fig. 100.— Sketch Showing Strut- 
ting for Lower Part of Section. 



184 



TUNNELING 



by inclined props arranged as shown by Fig. 103. When parts 
No. 2 are excavated the roof is strutted by inserting the trans- 
verse caps a, Fig. 100, the outer ends of which are carried by the 
system of struts 6, c^ d, and e. The longitudinal poling-boards 
supporting the ceiling and walls are held in place by the cap 
a and the side timber e. To stiffen the frames longitudinally 
of the tunnel, horizontal longitudinal struts are inserted between 
them. 

The excavation of the upper half of the tunnel section is 
strutted as in the Belgian method, with radial struts carrying 
longitudinal roof bars and transverse poling-boards. On ac- 
count of the enormous pressures developed by the treacherous 
soils in which only is the Italian method employed, the radial 
strutting frames and crown bars must be of great strength, 





Figs. 101 and lOlA. — Sketches Showing Construction of Centers, Italian Method. 

while the successive frames must be placed at frequent intervals, 
usually not more than 3 ft. After the masonry side walls have 
been built in the lower part of the excavation, longitudinal 
planks are laid against the side posts of the center bottom 
drift frames, to form an enclosure for the filling-in of parts 
No. 2. The object of this filling is principally to prevent 
the squeezing-in of the side walls. 

Centers. — Owing to the great pressures to be resisted in the 
treacherous soils in which the Italian method is used, the con- 
struction of the centers has to be very strong and rigid. Figs. 
101 and 10 lA show two common types of center construction 
used with this method. The construction shown in Fig. 101 
is a strong one where only pressures normal to the axis of the 
tunnel have to be withstood, but it is likely to twist under 



SPECIAL TKEACHEROUS GROUND METHOD 185 

pressures parallel to the axis of the tunnel. In the construc- 
tion shown by Fig. lOlA, special provision is made to resist 
pressures normal to the plane of the center or twisting pres- 
sures, by the strength of the transverse bracing extending hori- 
zontally across the center. 

Masonry. — The construction of the masonry lining begins 
with the invert, as indicated by Fig. 100, and is carried up to 
the roof of parts No. 2, as already indicated, and is then discon- 
tinued until the upper parts Nos. 4, 5, and 6 are excavated. 
The next step is to sink side trenches at the ends of part No. 7, 
which reach to the top of the completed side walls. This 
operation leaves the way clear to finish the side walls and to 
construct the roof arch in the ordinary manner of such work in 

tunneling. Since this method of 
tunneling is used only in very soft 
ground which yields under load, the 
usual practice is to construct the in- 
vert and side walls on a continuous 

Fig. 102. -Sketch Showing Invert foundation COUrSC of COUCretC aS iu- 
and Foundation Masonry, Italian dicatcd by Fis;. 102. The liuinpf is 
Method. n u -1^ • • • A 

usually built m successive rings, and 
the usual precautions are taken with respect to filling in the 
voids behind the lining. The thickness of the lining is based 
upon the figures for laminated clay of the third variety given 
in Table II. 

Hauling The system of hauling adopted with this method 

of tunneling is very simple, since the excavation of the various 
parts is driven only from 6 ft. to 10 ft. ahead, and the work pro- 
gresses slowly to allow for the construction of the heavy strutting 
required. To take away the material from the center bottom 
drift, narrow-gauge tracks carried by cross-beams between the 
side posts above the floor line are employed. This same 
narrow-gauge line is employed to take away a portion of parts 
No. 2, the remaining portion being left and used for the refill- 
ing after the bottom portion of the lining has been built, as 




186 



TUNNELING 



previously described. The upper half of the section being ex- 
cavated, as in the Belgian method, the system of hauling with 
inclined planes to the tunnel floor below, which is a character- 
istic of that method, may be employed. It is the more usual 




Fig. 103. — Sketch ShoAying Longitudinal Section of a Tunnel under Construction, 

Italian Method. 

practice, however, since the excavation is carried so little a dis- 
tance ahead and progresses so slowly, to handle the spoil from 
the upper part of the section by wheelbarrows which dump it 
into the cars running on the tunnel floor below. Hand labor 
is also used to raise the construction 
materials used in building the upper sec- 
tion. The tracks on the tunnel floor, 
besides extending to the front of the ad- 
vanced bottom center ^drift, have right and 
left switches to be employed in removing 
the refilling in parts No. 2, the spoil from 
the upper part of the section, and the 
material of part No. 7. Fig. 103 is a longi- 
tudinal section showing the plan of exca- 
vation and strutting adopted wdth the Italian method. 

Modifications. — It often happens that the filling placed be- 
tween the side walls and the planking, which is practically the 
space comprised by parts No. 2, is not sufficient to resist the 
inward pressure of the walls, and they tip inward. In these 
cases a common expedient is to substitute for the earth filling 




Fig. 104.— Sketch Showing 
Sequence of Excavation, 
Stazza TunneL 



SPECIAL TREACHEROUS GROUND METHOD 



187 



a temporary masonry arch sprung between the side walls 
with its feet near the bottom of the walls, and its crown, 
just below the level of their tops, as shown by Fig. 107. 
This construction was employed in the 
Stazza tunnel in Italy. In this tunnel 
the excavation was begun by driving the 
center drift, No. 1, Fig. 104, and immedi- 
ately strutting it as shown by Fig. 105. 
The other parts, Nos. 2 and 3, completing 
the lower portion of the section, were then 
taken out and strutted. While part No. 2 
Fig. 105. — Sketch Showing was being cxcavatcd at the bottom, and 

Metlied of strutting First .-i , j. r l^ • j. i •^l -i 

Drift, Stazza Tunnel. ^hc ccutcr part of the luvcrt built, the 
longitudinal crown bars carrying the roof 
of the excavation were carried temporarily by the inclined 
props shown by Fig. 106. After completing the invert and 
the side walls to a height of 2 or 3 ft., a thick masonry arch 
was sprung between the side walls, as shown in transverse 
section by Fig. 107, and in longitudinal section by Fig. 106. 
This arch braced the side walls against tipping inward, and 






Figs. 106 and 107. — Sketches Showing Temporary Strutting Arch Construction, 
Stazza Tunnel. 



carried short struts to support the crown bars. The haunches 
of the arch were also filled in with rammed earth. The upper 
half of the section was excavated, strutted, and lined as in 
the standard Italian method previously described. When the 
lining was completed, the arch inserted between the side walls 
was broken down and removed. 



188 TUNNELING 

Advantages and Disadvantages, — The great advantage claimed 
for the Italian method of tunneling is that it is built in two 
separate parts, each of which is separately excavated, strutted, 
and lined, and thus can be employed successfully in very 
treacherous soils. Its chief disadvantage is its excessive cost, 
which limits its use to tunnels through treacherous soils where 
other methods of timbering cannot be used. 

QUICKSAND TUNNELING. 

When an underground stream of water passes with force 
through a bed of sand it produces the phenomenon known as 
quicksand. This phenomenon is due to the fineness of the 
particles of sand and to the force of the water, and its activity 
is directly proportional to them. When sand is confined it 
furnishes a good foundation bed, since it is practically incom- 
pressible. To work successfully in quicksand, therefore, it is 
necessary to drain it and to confine the particles of sand so 
that they cannot flow away with the water. This observation 
suggests the mode of procedure adopted in excavating tunnels 
through quicksand, which is to drain the tunnel section by 
opening a gallery at its bottom to collect and carry away the 
water, and to prevent the movement or flowing of the sand by 
strutting the sides of the excavation with a tight planking. 

The sand having to be drained and confined as described, the 
ordinary methods of soft-ground tunneling must be employed, 
with the following modifications : 

(1) The first work to be performed is to open a bottom 
gallery to drain the tunnel. This gallery should be lined with 
boards laid close and braced sufficiently by interior frames to 
prevent distortion of the lining. The interstices or seams be- 
tween the lining boards should be packed with straw so as to 
permit the percolation of water and yet prevent the movement 
of the sand. 

(2) As fast as the excavation progresses its walls should 



SPECIAL TREACHEROUS GROUND METHOD 189 

be strutted by planks laid close, and held in position by interior 
framework; the seams between the plank should be packed 
with straw. 

(3) The masonry lining should be built in successive rings, 
and the work so arranged that the water seeping in at the sides 
and roof is collected and removed from the tunnel immediately. 

Excavation. — The best and most commonly employed meth( d 
of driving tunnels through quicksand is a modificauon of the 
Belgian method. At first sight it may appear a hazardous work 
to support the roof arch, as is the characteristic of this method, 
on the unexcavated soil below, when this soil is quicksand, but 
if the sand is well confined and drained the risk is really not 
very great. Next to the Belgian method the German method 
is perhaps the best for tunneling quicksand. In these compari- 
sons the shield system of tunneling is for the time being left 
out of consideration. This method will be described in suc- 
ceeding chapters. Whenever any of the systems of tunneling 
previously described are employed, the first task is always to 
open a drainage gallery at the bottom of the section. 

Assuming the Belgian method is to be the one adopted, the 
first work is to drive a center bottom drift, the floor of which 
is at the level of the extrados of the invert. This drift is im- 
mediately strutted by successive transverse frames made up of 
a sill, side posts, and a cap which support a close plank strut- 
ting or lining, with its joints packed with straw. Between the 
side posts of each cross-frame, at about the height of the 
intrados of the invert, a cross-beam is placed ; and on these cross- 
beams a plank flooring is laid, w^hich divides the drift horizon- 
tally into two sections, as shown by Fig. 108 ; the lower section 
forming a covered drain for the seepage water, and the upper 
providing a passageway for workmen and cars. The bottom 
drift is driven as far ahead as practicable, in order to drain the 
sand for as great a distance in advance of the work as possible. 
After the construction of the bottom drainage drift the excava- 
tion proper is begun, as it ordinarily is in the Belgian method 



190 



TUNNELING 




Fig, 108,— Sketch Showing 
Preliminary Drainage Gal- 
leries, Quicksand Method. 



by driving a top center heading, as shown by Fig. 108. This 
heading is deepened and widened after the manner usual to the 
Belgian method, until the top of the sec- 
tion is open down to the springing lines 
of the roof arch. To collect the seepage 
water from the center top heading it is 
provided with a center bottom drain con- 
structed like the drain in the bottom 
drift, as shown by Fig. 108. When the 
top heading is deepened to the level of 
the springing lines of the roof arch, its 
bottom drain is reconstructed at the new 
level, and serves to drain the full top 
section opened for the construction of the 
roof arch. This top drain is usually con- 
structed to empty into the drain in the bottom drift. 

Strutting. — The method of strutting the bottom drift has 
already been described. For the remainder of the excavation 
the regular Belgian method of radial roof strutting-frames is 

employed, as shown by Fig. 109. 
Contrary to what might be expected, 
the number of radial struts required 
is not usually greater than would be 
used in many other soils besides 
quicksand. Single-track railway tun- 
nels have been constructed through 
quicksand in several instances where 
the number of radial props required 
on each side of the center did not 
exceed four or five. It is necessary, 
however, to place the poling-boards 
very close together, and to pack the joints between them to 
prevent the inflow of the fine sand. In strutting the lower 
part of the section it is also necessary to support the sides with 
tight planking. This is usually held in place by longitudinal 




Fig. 109.— Sketch Showing Con- 
struction of Hoof Strutting 
Quicksand Method, 



SPECIAL TREACHEKOUS GROUND METHOD 



191 




Fig. 1 10. — Sketch Showing Construc- 
tion of Masonry Lining, Quicksand 
Method. 



bars braced by short struts against the inclined props employed 
to carry the roof arch when the material on which they origi- 
nally rested is removed. This side 
strutting is shown at the right 
hand of Fig. 110. 

Masonry. — As soon as the upper 
part of the section has been opened 
the roof arch is built with its feet 
resting on planks laid on the unex- 
cavated material below. This arch 
is built exactly as in the regular 
Belgian method previously de- 
scribed, using the same forms of 
centers and the same methods 
throughout, except that the poling- 
boards of the strutting are usually left remaining above the 
arch masonry. To prevent the possibility of water percolating 
through the arch masonry, many engineers also advise the 
plastering of the extrados of the arch with a layer of cement 
mortar. This plastering is designed to lead the water along 
the haunches of the arch and down behind the side walls. In 
constructing the masonry below the roof arch the invert is 
built first, contrary to the regular Belgian method, and the 
side walls are carried up on each side from the invert ma- 
sonry. Seepage holes are left in the invert masonry, and also 
in the side walls just above the intrados of the invert. At the 
center of the invert a culvert or drain is constructed, as shown 
by Fig. 110; inside the invert masonry. This culvert is com- 
monly made with an elliptical section with its major axis hori- 
zontal, and having openings at frequent intervals at its top. 
The thickness of the lining masonry required in quicksand is 
shown by Table II. 

Removing the Seepage Water. — After the tunnel is completed 
the water which seeps in through the weep-holes left in the ma- 
sonry passes out of the tunnel, following the direction of the 



192 TUNNELING 

descending grades. During construction, however, special 
means will have to be provided for removing the water from 
the excavation, their character depending upon the method of 
excavation and upon the grades of the tunnel bottom. When 
the excavation is carried on from the entrances only, unless the 
tunnel has a descendmg grade from the center toward each end, 
the tunnel floor in one heading will be below the level of the en- 
trance, or, in other words, the descending grade will be toward 
the point where Avork is going on, while at the opposite entrance 
the grade will be descending from the work. In the latter 
case the removal of the seepage water is easily accomphshed by 
means of a drainage channel along the bottom of the excavation. 
In the former case the water which drains toward the front is 
collected in a sump, and if there is not too great a difference in 
level between this sump and the entrance, a siphon may be used 
to remove it. Where the siphon cannot be used, pumps are 
installed to remove the water. When the tunnel is excavated 
by shafts the condition of one high and one low front, as com- 
pared with the level at the shaft, is had at each shaft. Gene- 
rally, therefore, a sump is constructed at the bottom of the 
shaft; the culvert from the high front drains directly to the 
shaft sump, while the water from the low-front sump is either 
siphoned or pumped to the shaft sump. From the shaft sump 
the water is forced up the shaft to the surface by pumps. 

THE PILOT METHOD. 

The pilot system of tunneling has been successfully em- 
ployed in constructing soft-ground sewer tunnels in America 
by the firm of Anderson & Barr, which controls the patents. 
The most important work on which the system has been em- 
ployed is the m^ain relief sewer tunnel built in Brooklyn, N.Y., 
in 1892. This work comprised 800 ft. of circular tunnel 15 ft. 
in diameter, 4400 ft. 14 ft. in diameter, 3200 ft. 12 ft. in 
diameter, and 1000 ft. 10 ft. in diameter, or 9400 ft. of tunnel 



SPECIAL TEEACHEROUS GROUND METHOD 



193 



altogether. The method of construction by the pilot system is 
as follows : 

Shafts large enough for the proper conveyance of materials 
from and into the tunnel are sunk at such places on the line of 
work as are most convenient for the purpose. From these 
shafts a small tunnel, technically a pilot, about 6 ft. in diameter, 
composed of rolled boiler iron plates riveted to light angle irons on 
four sides, perforated for bolts, and bent to the required radius 
of the pilot, is built into the central part of the excavation on 
the axis of the tunnel. This pilot is generally kept about 30 ft. 
in advance of the completed excavation, as shown by Fig. 111. 
The material around the exterior of the pilot is then excavated, 
using the pilot as a support for braces which radiate from it and 




Bracing." ' Arch ConstrOction. 

Fig. 111. — Sketch Showing Pilot Method of Tunneling. 



secure in position the plates of the outside shell which holds 
the sand, gravel, or other material in place until the concentric 
rings of brick masonry are built. Ribs of T-iron bent to the 
radius of the interior of the brick work, and supported by the 
braces radiating from the pilot, are used as centering supports 
for the masonry. On these ribs narrow lagging-boards are laid 
as the construction of the arch proceeds, the braces holding the 
shell plates and the superincumbent mass being removed as the 
masonry progresses. The key bricks of the arches are placed 
in position on ingeniously contrived key-boards, about 12 ins. in 
width, which are fitted into rabbeted lagging-boards one after 
another as the key bricks are laid in place. After the masonry 
has been in place at least twenty-four hours, allowing the cement 



194 TUNNELING 

mortar time to set, the braces, ribs, and lagging which support 
it are removed. In the meantime the excavation, bracing, pilot, 
and exterior shell have been carried forward, preparing the way 
for more masonry. The top plates of the shell are first placed 
in position, the material being excavated in advance and sup- 
ported by light poling-boards ; then the side-plates are butted 
to the top and the adjoining side-plates. In the pilot the plates 
are united continuously around the perimeter of the circle, 
while in the exterior shell the plates are used for about one- 
third of the perimeter on top, unless treacherous material is 
encountered, when the plates are continued down to the spring- 
ing lines of the arch. This iron lining is left in place. The 
bottom is excavated so as to conform to the exterior hues of 
the masonry. The excavation follows so closely to the outer 
lines of the normal section of the tunnel that very little loss 
occurs, even in bad material ; and there is no loss where suffi- 
cient bond exists in the material to hold it in place until the 
poling-boards are in position. 

In the Brooklyn sewer tunnel work, previously mentioned, 
the pilot was built of steel plates | in. thick, 12 ins. wide, and 
37^ ins. long, rolled to a radius of 3 ft. Steel angles 4x4^ ins. 
were riveted along all four sides of each plate, and the plates 
were bolted together by |-in. machine-bolts. The plates weighed 
136 lbs. each, and six of them were required to make one com- 
plete ring 6 ft. in diameter. In bolting them together, iron 
shims were placed between the horizontal joints to form a 
footing for the wooden braces for the shell, which radiate from 
the pilot. The shell plates of the 15-ft. section of the tunnel 
were of No. 10 steel 12 ins. wide and 37 ins. long, with steel 
angles 2^ x 2i^ x f ins., riveted around the edges the same as for 
the pilot, and put together with |-in. bolts. These plates 
weighed 61 lbs. each, and eighteen of them were required to 
make one complete ring 15 ft. in diameter. The plates for the 
12-ft. section were No. 12 steel 12 ins. wide with 2x 2 x i-in. 
angles. Seventeen plates were required to make a complete ring. 



OPEN-CUT TUNNELING METHODS 195 



CHAPTER XVI. 

OPEN-CUT TUNNELING METHODS; TUNNELS 

UNDER CITY STREETS; BOSTON SUBWAY 

AND NE^V YORK RAPID TRANSIT. 



OPEN-CUT TUNNELING. 

When a tunnel or rapid-transit subway has to be constructed 
at a small depth below the surface, the excavation is generally 
performed more economically by making an open cut than by 
subterranean tunneling proper. The necessary condition of 
small depth which makes open-cut tunneling desirable is most 
generally found in constructing rapid-transit subways or tun- 
nels under city streets. This fact introduces the chief difficul- 
ties encountered in such work, since the surface traffic makes it 
necessary to obstruct the streets as little as possible, and has 
led to the development of the several special methods commonly 
employed in performing it. 

Subways are usually constructed under and along important 
streets where electric cars are running. The engineers have 
taken advantage of the presence of these hnes to facilitate the 
construction of subways. In New York, for instance, the tracks 
of the electric Hnes were supported by cast-iron yokes 4 or 5 ft. 
apart and were surrounded by concrete, leaving only a large 
hollow space in the middle for the wires and trolleys. The rails 
from 40 to 60 ft. long formed almost a soHd concrete structure 
for their entire length. The tracks and the street surface were 
supported by horizontal beams inserted underneath the tracks. 
These were the caps of bents constructed underground whose 
rafters were finally resting on the subgrade of the proposed 
subway. 



196 TUNNELING 

The various methods for constructing the subways may be 
classified as follows: (1) The single wide trench method; (2) the 
single narrow longitudinal trench method; (3) the parallel longi- 
tudinal trench method; (4) the shce method. 

Single Longitudinal Trench. — The simplest manner by which 
to construct open-cut tunnels is to open a single cut or trench 
the full width of the tunnel masonry. This trench is strutted 
by means of side sheetings of vertical planks, held in place by 
transverse braces extending across the trench and abutting 
against longitudinal timbers laid against the sheeting plank. 
The lining is built in this trench, and is then filled around and 
above with well-rammed earth, after which the surface of the 
ground is restored. An especial merit of the single longitudinal 
trench method of open-cut tunneling is that it permits the 
construction of the lining in a single piece from the bottom up, 
thus enabhng better workmanship and stronger construction 
than when the separate parts are built at different times. The 
great objection to the method w^hen it is used for building sub- 
ways under city streets is, that it occupies so much room that the 
street usually has to be closed to regular traffic. For this reason 
the single longitudinal trench method is seldom employed, except 
in those portions of city subways which pass under public squares 
or parks where room is plenty. 

This method was followed in the construction of the New 
York subway, Section 2, along Elm St., a new street to be opened 
to traffic after the subway had been completed, and at other 
points where local conditions allowed it. 

A modification of this method was used in Contract Section 6, 
on upper Broadway. The street at this point is very wide, so 
by opening a trench as wide as the proposed four-track line of 
the subway there still remained room enough for ordinary 
traffic. The electric car tracks were supported by means of 
trusses 60 or 70 ft. long, which were laid in couples parallel to 
the tracks and which rested on firm soil. The soil under the 
car tracks was removed, beginning with transversal cuts to 



OPEN-CUT TUNNELING METHODS 



19T 



receive the needles which were tied to the lower chord of the 
trusses by means of iron stirrups. After the excavation had 
reached the subgrade, posts were erected to support the needles 
thus forming bents upon which the tracks rested. The trusses 
were removed and advanced to another section of the tunnel, 
and, in the clear space left, the subway was built from founda- 
tion up. 

The Single Narrow Longitudinal Trench. — This method was 
used on Contract Section 5, of the New York subway in order 
to comply with the peculiar conditions of the traffic along 42nd 
St. On this street, on account of the New York Central Station, 
there is a constant heavy traffic, while pedestrians use the 
northern sidewalks almost exclusively. A single longitudinal 
trench was then opened along the south side, and from this 
trench all the work of excavation and construction was carried 
on. At first the steel structure of the subway was erected in the 
trench and then a small heading was driven and strutted under 
and across the surface-car tracks. Afterward heavy I-beams 
were inserted, which rested with one end on top of the steel 
bents and the other end blocked to 
the floor of the excavation. These 
I-beams were located 5 ft. apart 
and they supported the surface of 
the street by means of longitudi- 
nal planks. The soil was removed 
from the wide space underneath the 
I-beams and the subway was con- 
structed from the foundation up. 
When the structure had been com- 
pleted, the packing was placed be- 
tween the roof of the structure and 
the surface of the street, the I-beams withdrawn and the voids 
filled in. 

Parallel Longitudinal Trenches. — The parallel longitudinal 
trench method of open-cut tunneling consists in excavating two 




Fig. 112. — Diagram Showing Se- 
quence of Construction in Open- 
Cut Tunnels. 



198 



TUNNELING 




Fig. 113. — Sketch Showing Method of Timbering Open- 
Cut Tunnels, Double Parallel Trench Method. 



narrow parallel trenches for the side walls, leaving the center 
core to be removed after the side walls have been built. The 
diagram, Fig. 112, shows the sequence of operations in this 

method. The two 
ULLIliillJJJiJiJiliilimuillM trenches No. 1 are 

first excavated a little 
wider than the side 
wall masonry, and 
strutted as show^n by 
Fig. 113. At the bot- 
toms of these trenches 
a foundation course 
of concrete is laid, as 
shown by Fig. 114, 
if the ground is soft; 
or the masonry is 
started directly on the natural material, if it is rock. From 
the foundations the walls are carried up to the level of the 
springing lines of the roof arch, if an arch is used; or to the 
level of its ceiling, if a flat roof is used. After the completion 
of the side walls, the portion of the exca- 
vation shown at No. 2, Fig. 112, is removed 
a sufficient depth to enable the roof arch 
to be built. When the arch is completed, 
it is filled above with well-rammed earth, 
and the surface is restored. The excavation 
of part No. 3 inclosed by the side walls 
and roof arch is carried on from the en- 
trances and from shafts left at intervals 
along the line. 

A modification of the method just de- 
scribed was employed in constructing the Paris underground 
railways. It consists in excavating a single longitudinal trench 
along one side of the street, and building the side wall in it 
as previously described. When this side wall is completed to 




Fig. 114. — Side-Wall 
Foundation Con- 
struction Open-Cut 
Tunnels. 



OPEN-CUT TUNNELING METHODS 199 

the roof, the right half of part No. 2, Fig. 112, is excavated to 
the line AB, and the right-hand half of the roof arch is built. 
The space above the arch is then refilled and the surface of the 
street restored, after which the left-hand trench is dug and 
the side wall and roof-arch masonry is built just as in the 
opposite half. Generally the work is prosecuted by opening up 
lengths of trench at considerable intervals along the street and 
alternately on the left- and right-hand sides. By this method 
one-half of the street width is everywhere open to traffic, the 
travel simply passing from one side of the street to the other 
to avoid the excavation. When the Hning has been completed,, 
the center core of earth inclosed by it is removed from the 
entrances and shafts, leaving the tunnel finished except for the 
invert and track construction, etc. 

Another modification of the parallel longitudinal trenches 
method was used in the construction of the New York subway. 
A narrow longitudinal trench was excavated on one side of the 
street near the sidewalk. Meanwhile the pavement of half of 
the street was removed and a wooden platform of heavy planks, 
supported by longitudinal beams which were buried in the 
ground, was substituted. Then small cuts underneath the car 
tracks were directed from the side trench and heavy beams or 
needles were placed in these cuts, which also reached the longi- 
tudinal beams of the wooden platform. The needles were 
wedged and blocked to the car track structure and the beams. 
They were temporarily supported by cribs built from under- 
neath as the excavation progressed. AVhen the subgrade was 
reached, vertical and batter posts were inserted to support the 
needles, thus forming regular timber bents underground. In 
the space thus left open the subway was constructed to the 
middle of the street. While the work was going on as described, 
another longitudinal narrow trench was excavated at some 
distance on the other side of the street. From this trench, the 
work of constructing the other half of the subway was carried 
on in the manner just described. After the work had been 



200 TUNNELING 

completed, the timbers removed, the voids filled in and the 
pavement of the street restored, another equal section was at- 
tacked on both sides of the street. 

Transverse Trenches. — The transverse trench or ^' slice " 
method of open-cut tunneling has been employed in one work, 
the Boston Subway. This method is described in the specifica- 
tions for the work prepared by the chief engineer, Mr. H. A. 
Carson, M. Am. Soc. C. E., as follows: — 

''Trenches about 12 ft. wide shall be excavated across the 
street to as great a distance and depth as is necessary for the 
construction of the subway. The top of this excavation shall 
be bridged during the night by strong beams and timbering, 
whose upper surface is flush with the surface of the street. 
These beams shall be used to support the railway tracks as well 
as the ordinary traffic. In each trench a small portion or slice 
of the subway shall be constructed. Each slice of the subway 
thus built is to be properly joined in due time to the contiguous 
shces. The contractor shall at all times have as many slice- 
trenches in process of excavation, in process of being filled with 
masonry, and in process of being back-filled with earth above 
the completed masonry, as is necessary for the even and steady 
progress of the work towards completion at the time named in 
the contract." 

In regard to the success of this method Mr. Carson, in his 
fourth annual report on the Boston Subway work, says : 

'' The method was such that the street railway tracks were 
not disturbed at all, and the whole surface of the street, if de- 
sired, was left in daytime wholly free for the normal traffic." 

Tunnels on the Surface. — It occasionally happens when 
filling-in is to take place in the future, or where landslides are 
liable to bury the tracks, that a railway tunnel has to be built 
on the surface of the ground. In such cases the construc- 
tion of the tunnel consists simply in building the lining of the 
section on the ground surface with just enough excavation to 
secure the proper grade and foundation. Generally the lining 



OPEN-CUT TUNNELING METHODS 201 

is finished on the outside with a waterproof coating, and is 
sometimes banked and partly covered with earth to protect the 
masonry from falHng stones and similar shocks from other 
causes. A recent example of tunnel construction of this char- 
acter was described in " Engineering News "of Sept. 8, 1898. 
In constructing the Golden Circle Railroad, in the Cripple Creek 
mining district of Colorado, the line had to be carried across a 
valley used as a dumping-ground for the refuse of the surround- 
ing mines. To protect the line from this refuse, the engineer 
constructed a tunnel lining consisting of successive steel ribs, 
filled between with masonry. 

Concluding Remarks. — From the fact that the open-cut 
method of tunneling consists first in excavating a cut, and sec- 
ond in covering this cut to form an underground passageway, 
it has been named the '' cut-and-cover " method of tunneling. 
The cut-and-cover method of tunnehng is almost never employed 
elsewhere than in cities, or where the surface of the ground has 
to be restored for the accommodation of traffic and business. 
When it is not necessary to restore the original surface, as is 
usually the case with tunnels built in the ordinary course of 
railway work, it would obviously be absurd to do so except in 
extraordinary cases. In a general way, therefore, it may be said 
that the cut-and-cover method of construction is confined to the 
building of tunnels under city streets; and the discussion of 
this kind of tunnels follows logically the general description of 
the open-cut method of tunneling which has been given. 

TUNNELS UNDER CITY STREETS. 

The three most common purposes of tunnels under city streets 
are : to provide for the removal of railway tracks from the street 
surface, and separate the street railway traffic from the vehicular 
and pedestrian traffic; to provide for rapid transit railways 
from the business section to the outlying residence districts 
of the city; and to provide conduits for sewage or subways for 
water and gas mains, sewers, wires, etc. Within recent years 



202 TUNNELING 

the greatest works of tunneling under city streets have been 
designed and carried out to furnish improved transit facilities. 

Conditions of Work. — The construction of tunnels under city 
streets may be divided into two classes, which may be briefly 
defined as shallow tunnels and deep tunnels. Shallow tunnels, 
or those constructed at a small depth beneath the surface, are 
usually built by one of the cut-and-cover methods; deep tun- 
nels, or those built at a great depth, beneath the surface are 
constructed by any of the various methods of tunneling de- 
scribed in this book, the choice of the method depending upon 
the character of the material penetrated, and the local conditions. 

In building tunnels under city streets the first duty of the 
engineer is to disturb as little as possible the various existing 
structures and the activities for which these structures and the 
street are designed. The character of the difficulties encoun- 
tered in performing this duty will depend upon the depth at 
which the tunnel is driven.. In constructing shallow tunnels 
by the cut-and-cover method care has to be taken first of all 
not to disturb the street traffic any more than is absolutely 
necessary. This condition precludes the single trench method 
of open cut tunneling in all places where the street traffic is at 
all dense, and compels the engineer to use the methods employed 
in Paris and New York, as previously described, or else the 
transverse trench or slice method employed in the Boston 
Subway. 

These methods have to be modified when the work is done 
on streets having underground trolley and cable roads, and in 
v/hich are located gas and water pipes, conduits for wires, etc. 
Where underground trolley or cable railways are encountered, 
a common mode of procedure is to excavate parallel side trenches 
for the side walls, and turn the roof arch until it reaches the 
conduit carrying the cables or wires. The earth is then removed 
from beneath the conduit structure in small sections, and the 
arch completed as each section is opened. As fast as the arch 
is completed the conduit' structure is supported on it. Where 



OPEN-CUT TUNNELING METHODS 203 

pipes are encountered they may be supported by means of chains, 
suspending them from heavy cross-beams, or by means of 
strutting, or they may be removed and rebuilt at a new level. 
Generally the conditions require a different solution of this 
problem at different points. 

Another serious difficulty of tunneling under city streets 
arises from the danger of disturbing the foundations of the 
adjacent buildings. This danger exists only where the depth 
of the tunnel excavation extends below the depth of the build- 
ing foundations, and where the material penetrated is soft 
ground. Where the tunnel penetrates rock there is no danger 
of disturbing the building foundations. To prevent trouble of 
this character requires simply that the excavation of the tunnel 
be so conducted that there is no inflow of the surrounding mate- 
rial, which may, by causing a settlement of the neighboring 
material, allow the foundations resting on it to sink. 

The Baltimore Belt tunnel, described in a preceding chap- 
ter, is an example of the method of work adopted in construct- 
ing a tunnel under city streets through very soft ground. This 
may be classed as a deep tunnel. Another method of deep 
tunneling under city streets is the shield method, examples of 
which are given in a succeeding chapter. Two notable examples 
of cut-and-cover methods of tunnehng are the Boston Subway 
and the New York Rapid Transit Ry., a description of which 
follows. 

Boston Subway. — The Boston Subway may be defined as 
the underground terminal system of the surface street railway 
system of the city, and as such it comprises various branches, 
loops, and stations. The subway begins at the Public Garden 
on Boylston St., near Charles St., and passes with double tracks 
under Boylston St. to its intersection with Tremont St., where 
it meets the other double-track branch, passing under Tremont 
St. and beginning at its intersection with Shawmut Ave. From 
their intersection at Tremont and Boylston streets the two 
double-track branches proceed under Tremont St. with four 



204 



TUNNELING 



tracks to Scollay Square. At ScoUay Square the subway 
divides again into two double-track branches, one passing under 
Hanover St., and the other under Washington St. At the 
intersection of Hanover and Washington streets the two double- 
track branches combine again into a four-track line, which runs 
under Washington St. to its terminus at Haymarket Square, 
where it comes to the surface by means of an incline. The sub- 
way, therefore, has three portals or entrances, located respec- 
tively at Boylston St., Shawmut Ave., and Haymarket Square. 
It also has five stations and two loops, the former being located 
at Boylston St., Park St., Scollay Square, Adams Square, and 
Haymarket Square, and the latter at Park St. and Adams 
Square. The total length of the subway is 10,810 ft. 

Material Penetrated. — The material met with in construct- 
ing the subway was alluvial in character, the lower strata being 
generally composed of blue clay and sand, and the upper strata 
of more loose soil, such as loam, oyster shells, gravel, and peat. 
At many points the material was so stable that the walls of 
the excavation would stand vertical for some time after excava- 
tion. Surface water was encountered, but generally in small 
quantities, except near the Boylston St. portal, where it was 
so plentiful as to cause some trouble. 

Cross-Section. — The subway being built for two tracks in 

some places and for four 
tracks in other places, it was 
necessary to vary the form 
and dimensions of the cross- 
section. The cross-sections 
actually adopted are of three 
types. Fig. 115 shows the 
section known as the wide- 
arch type, in which the lining 
is solid masonry. The second type was known as the double- 
barrel section, and is shown by Fig. 116. The third type of 
section is shown by Fig. 116. The lining consists of steel col- 




FiG. 115. — Wide Arch Section, Boston Subway. 



OPEN-CUT TUNNELING METHODS 



206 



umns carrying transverse roof girders, the roof girders being 
filled between with arches, and the wall columns having concrete 
walls between them. The wide-arch type and the double-barrel 
type of sections were employed in some portions of the Tremont 
St. line, where the traffic was very dense, since it was possible 
to construct them without opening the street. Much of the 
wide-arch line was constructed by the use of the roof shield, 
w^hich is described in the succeeding chapter on the shield system 
of tunneling. 

Methods of Construction. — Several different methods were 




Fig. 116. — Double-Barrel Section, Boston Subway. 



employed in constructing the subway. Where ample space 
was available, the single wide trench method of cut-and-cover 
construction was employed, the earth being removed as fast as 
excavated. In the streets, except where regular tunneling was 
resorted to, the parallel trench or transverse trench cut-and- 
cover methods were employed. 

In the transverse trench method, trenches about 12 ft. wide 



206 



TUNNELING 



were excavated across the street, their length being equal to 
the extreme transverse width of the tunnel lining, and their 
depth being equal to the depth of the tunnel floor. These 
trenches were begun during the night, and immediately roofed 



Concrei 
Cross Section ctf Side Wall, 



'i-Concrefe 

^"- WaterproofinaSrPtastei 

' ''Ribbed Tile 



^, Tar Contrets-'%^ 

'Fine Brohen Snne--:^ 
W.proofing'S Plaster 
HAYMARKET SQUARE Cross Section of Roof, 



CofKPfff 

■Brick 



nibbed 
Tile- 



li!^^<^0^:^^::'i^M I 



'Drain 




Fig. 117. — Four-Track Rectangular Section, Boston Subway. 

over with a timber platform flush with the street surface. Under 
these platforms the excavation was completed and the lining 
built. As each trench or '' slice " was completed, the street 
above it was restored and the platform reconstructed over 
the succeeding trench or slice. During the construction of 




Fig. 118. — Section Showing Slice Method of Construction, Boston Subway. 

each slice the street traffic, including the street cars, was carried 
by the timber platform. 

In the parallel trench method, short parallel trenches were 
dug for the opposite side walls, and also for the intermediate 
columns, and completely roofed over during the night. Under 



OPEN-CUT TUNNELING METHODS 207 

this roofing the masonry of the side walls and column founda- 
tions and the columns themselves were erected. When the 
side walls and columns had been erected, the surface of the 
street between them was removed, the roof beams laid, and a 
platform covering erected, as shown by Fig. 118. This roofing 
work was also done at night. The subsequent work of build- 
ing the roof arches, removing the remainder of the earth, and 
constructing the invert, was carried on underneath the plat- 
form covering which carried the street traffic in the meantime. 
The successive repetition of the processes described constructed 
the subway. 

Where the traffic was very dense on the street above, tunnel- 
ing was resorted to. For small portions of this work the ex- 
cavation was done in the ordinary way, using timber strutting, 
but much the greater portion of the tunnel work was performed 
by means of a roof shield. In the latter case, the side walls 
were first built in small bottom side drifts and were fitted with 
tracks on top to carry the roof shield. The construction and 
operation of this shield are described fully in the succeeding 
chapter on the shield system of tunneling. 

Masonry. — The masonry of the inclined approaches to the 
subway consists simply of two parallel stone masonry retaining 
walls. In the wide-arch and double-barrel tunnel sections, the 
side walls are of concrete and the roof arches are of brick masonry. 
In the other parts of the subway the masonry consists of brick 
jack arches sprung between the roof beams and covered with 
concrete, of concrete walls embedding the side columns, and 
of the concrete invert and foundations for the columns. Figs. 
115 to 118 inclusive show the general details of the masonry 
work for each of the three sections. The inside of the lining 
masonry is painted throughout with white paint. 

Stations. ^^ The design and construction of the stations for 
the Boston Subway were made the subjects of considerable 
thought. All the stations consist of two island platforms of 
artificial stone having stairways leading to the street above. 



208 TUNNELING 

The platforms are made 1 ft. higher than the rails. The station 
structure itself is built of steel columns and roof beams with 
brick roof arches and concrete side walls. Its interior is lined 
with white enameled tiles. The intermediate columns are cased 
with wood, and have circular wooden seats at their bottoms. 
Each stairway is covered by a light housing, consisting of a 
steel framework with a copper covering and an interior wood 
and tile finish. 

Ventilation. — The subway is ventilated by means of exhaust 
fans located in seven fan chambers, some of which contain 
two fans, and others only one fan. Each of the fans has a 
capacity of from 30,000 to 37,000 cu. ft. of air per minute, and 
is driven by electric motor, taking current from the trolley 
wires. This system of ventilation has worked satisfactorily. 

Disposal of Rain Water. — The rain water which enters the 
subway from the inclined entrances, together with that from 
leakage, is lifted from 12 ft. to 18 ft. by automatic electric pumps 
to the city sewers. The subway has pump-wells at the Public 
Garden, at Eliot St., Adams Square, and Haymarket Square. 
In each of these wells are two vertical submerged centrifugal 
pumps made entirely of composition metal. In each chamber 
above, are two electric motors operating the pumps. Each 
motor is started and stopped according to the height of water 
by means of a float and an automatic release starting box. 
The floats are so placed that only one pump is usually brought 
into use. The other, however, comes into service in case the 
first pump is out of order or the water enters more rapidly than 
one pump can dispose of it. In the latter case, both motors 
continue to run until the same low level has been reached. 

Very little dampness except from atmospheric condensation 
is to be found on the interior walls or roof of the subway, al- 
though numerous discolored patches, caused by dampness and 
dust, may be seen on some parts of the walls. Substantially all 
of the leakage comes through the small drains in the invert 
leading from hollows left in the side walls. Careful measure- 



OPEN-CUT TUNNELING METHODS 209 

ment was taken at the end of an unusually wet season to de- 
termine the actual amount of leakage, and the total amount for 
the entire subway was found to be about 81 gallons per minute. 
Estimated Quantities. — The estimated quantities of material 
used in constructing the subway were as follows : 

Excavation 369,450 cu. yds. 

Concrete 75,660 " " 

Brick 11,105 " " 

Steel 8,105 tons 

Granite 2,285 cu. yds. 

Piles 117,925 lin. ft. 

Ribbed tiles 12,440 sq. yds. 

Plaster 88,190 " " 

Waterproofing (asphalt coating) .... 117,980 " " 

Artificial stone 6,790 " " 

Enameled brick 2,210 " " 

Enameled tiles 2,855 " " 

Cost of the Subway. — The estimated cost of the subway made 
before the work was begun was approximately $4,000,000, and 
the cost of construction did not exceed $3,700,000. This in- 
cludes ventilating and pump chambers, changes of water and 
gas pipes, sewers and other structures, administration, engineer- 
ing, interest on bonds, and all cost whatsoever. Dividing this 
number by the total length we obtain a cost per linear foot of 
$342.30. 

New York Rapid Transit Railway. — The project of an under- 
ground rapid transit railway to run the entire length of Man- 
hattan Island was originated some years previous to 1890. In 
1894, however, a Rapid Transit Commission was appointed to 
prepare plans for such a road, and after a large amount of trouble 
and delay this commission awarded the contract for construction 
to Mr. John B. McDonald of New York City, on Jan. 15, 1900. 

Route. — The road starts from a loop which encircles the 
City Hall Park. Within this loop the tunnel construction is 
two-track; but where the main line leaves the loop, all four tracks 
come to the same level, and continue side by side thereafter 



210 TUNNELING 

except at the points which will be noted as the description 
proceeds. Proceeding from the loop, the four-track line passes 
under Center and Elm Streets. It continues under Lafayette 
Place, across Astor Place and private property between Astor 
Place and Ninth St. to Fourth Ave. The road then passes 
under Fourth and Park Avenues until 42d St. is reached. At 
this point the Hne turns west along 42d St., which it follows to 
Broadway. It turns northward again under Broadway to the 
boulevard, crossing the Circle at 59th St. The road then follows 
the boulevard until 97th St. is reached, where the four-track 
line is separated into two double-track lines. 

At a suitable point north of 96th St. the outside tracks rise 
so as to permit the inside tracks, on reaching a point near 103d St., 
to curve to the right, passing under the north-bound track, 
and to continue thence across and under private property to 
104th St. From there the two-track tunnel goes under 104th St. 
and Central Park to 110th St., near Lenox Ave.; thence under 
Lenox Ave to a point near 142d St.; thence across and under 
private property and the intervening streets to the Harlem River. 
The road passes under the Harlem River and across and under 
private property to 149th St., which street it follows to Third 
Ave., and then passes under Westchester Ave., where, at a con- 
venient point, the tracks emerge from the tunnel and are carried 
on a viaduct along and over Westchester Ave., Southern Boule- 
vard, and Boston Road to Bronx Park. This portion of the line, 
from 96th St. to Bronx Park, is known as the East Side Line. 

From the northern side of 96th St. the outside tracks rise 
and after crossing over the inside tracks they are brought to- 
gether on a location under the center line of the street and pro- 
ceed along under the boulevard to a point between 122d and 
123d Streets. At this point the tracks commence to emerge 
from the tunnel, and are carried on a \daduct along and over 
the boulevard at a point* between 134th and 135th Streets, where 
they again pass into the tunnel under and along the boulevard 
and Eleventh Ave. to a point about 1350 ft. north of the center 



OPEN-CUT TUNNELING METHODS 211 

line of 190th St. There the tracks again emerge from the tunnel, 
and are carried on a viaduct across and over private property 
to El wood St., and over and along El wood St. to Kingsbridge St. 
to Kingsbridge Ave., private property, the Harlem Ship Canal 
and Spuyten Duyvil Creek, private property, Riverdale Ave., 
and Broadway to a terminus near Van Cortland Park. That 
portion of the line from 96th St. to the above-mentioned ter- 
minus at Van Cortland Park is known as the West Side Line. 

The total length of the rapid transit road, including the parts 
above and below the surface ground of the streets, as well as 
both the East and West Side Lines, is about 22^ miles. 

Material Penetrated. — The soil through which the road was 
excavated was a varied one. The lower portion of the road, or 
the part including the loop up to nearly Fourth St., was excavated 
through loose soil, but from Fourth St. to the ends it was ex- 
cavated in rock. The loose soil forming the southern part of 
Manhattan Island is chiefly composed of clay, sand, and old 
rubbish — a soil very easy to excavate. Water was met at 
some points, but not in such quantities as to be a serious in- 
convenience. From Fourth St. to the ends of both the east 
and west side lines, the soil was chiefly composed of rock of 
gneissoid and mica-schistose character, these rocks prevailing 
nearly throughout the whole of Manhattan Island. The rock, 
as a rule, was not compact, but full of seams and fissures, and 
at many points it was found disintegrated and alternated with 
strata of loose soils, and even pockets of quicksand were met 
with along the line of the road. 

Cross-Sections. — The section of the underground road is of 
three different types, — the rectangular, the barrel-vault, and 
the circular. The rectangular section. Fig. 119, is used for the 
greater part of the road, of which a portion is for four tracks and 
a portion for two tracks. The dimensions adopted for the four 
tracks are 50 X 13 ft., and for the double tracks 25 X 13 ft. 
The barrel-vault section, composed of a polycentric arch, having 
the flattest curve at the crown, has been adopted for the tunnels 



212 



TUNNELING 



under Park Avenue — while the semicircular arch is used for 
all the other portions of the road to be tunneled. The circular 
section of 15-ft. diameter is used under the Harlem River, and 
being for single track, two parallel tunnels were built side by side. 
The main line from the City Hall loop to about 102d St. con- 
sists of four tracks built side by side in one conduit, except for 
that portion under the present Fourth Ave. tunnel where two 
parallel double-track tunnels are employed. The West Side 
Line will consist of double tracks laid in one conduit, except 
across Manhattan St. and beyond 190th St., where it is carried 




Water Dvofinq MMmumThi'c/iness iobe 8.' 

' Thichness Increased in Bad &round 

Fig. 119. — Double-Track Section, New York Rapid Transit Railway. 



on an elevated structure. The East Side Line consists of a 
double-track tunnel driven from 102d St., and the boulevard 
under Central Park to 110th St. and Lenox Ave., and two 
parallel circular tunnels excavated under the Harlem River, — 
the other portions of the road being double-track, subway and 
elevated structure. 

Methods of Excavation. — Both the double- and four-track 
subway were built by using the different varieties of the cut-and- 
cover method. The single wide-trench method was used for 
the construction of the double-track line and also for the con- 
struction of the four-track line where the local conditions allowed 



OPEN-CUT TUNNELING METHODS 213 

it. The single narrow-trench method was used for the con- 
struction of the four-track subway at 42d St., to meet with the 
pecuHar conditions of the traffic. Almost the total length of 
the four-track line of the subway was built by means of the two 
parallel side trenches. The slice method, so successfully em- 
ployed in the Boston Subway, was used only on 42d St. west 
of 6th Avenue. 

Lining. — The lining of the subway is of concrete, carried 
by a framework of steel. The floor consists of a foundation 
layer of concrete at least eight inches thick on good founda- 
tion, but thicker, according to conditions, where the foundation 
is bad. On top of this is placed another layer of concrete, with 
a layer of waterproofing between the two. In this top layer 
are set the stone pedestals for the steel columns, and the mem- 
bers making up the tracks. 

In the four-track subway, the steel framework consists of 
transverse bents of columns, and I-beams spaced about five feet 
apart along the tunnel. The three interior columns of each 
bent are built-up bulb-angle and plate columns of H-section. 
The wall columns are I-beams, as are also the roof beams; be- 
tween the I-beams, wall columns, and roof beams there is a 
concrete filling, so that the roof of the subway will be made 
up of concrete arches resting on the flanges of the I-beams of 
the roof. The concrete used is of one part Portland cement, 
two parts sand, and four parts broken stones. The double- 
track subway is built in the -same way, except that only one 
column is placed between the tracks for the support of the 
roof. 

^All the concrete masonry of the roof, foundations, and side 
walls contains a layer of waterproofing, so as to keep perfectly 
dry the underground road, and prevent the percolation of water. 
This waterproofing is made up as follows : On the lowest stratum 
of concrete, whose surface is made as smooth as possible, a layer 
of hot asphalt is spread. On this asphalt are immediately laid 
sheets or rolls of felt ; another layer of hot asphalt is then spread 



214 



TUNNELING 



over the felt, and then another layer of felt laid, and so on, until 
no less than two, and no more than six, layers of felt are laid, 
with the felt between layers of asphalt. On top of the upper 
surface of asphalt the remainder of the concrete is put in place 
so as to reach the required thickness of the concrete wall. 

Tunnels. — When the distance between the roof of the pro- 
posed structure and the street was 20 ft. or over, the Standard 
Subway construction was replaced by tunnels. Three important 
tunnels have been constructed along the line of the New York 
Rapid Transit and these are located between 33d and 42d Streets 
on Park Ave., under Central Park northeast of 104th St. and 
under Broadway north of 152d St. The Park Ave. construction 
(Fig. 120) consists of two parallel double-track tunnels, located 





- /7'(7' 



Fig. 120. — Park Avenue Deep Tunnel Construction, New York Rapid Transit Railway. 

on each side of the street, and about 10 ft. below the present 
tunnel. The soil being composed of good rock, the tunnels were 
driven by a wide heading, and one bench, since no strutting 
was required, and the masonry lining, even of the roof, was left 
far behind the front of the excavation. The masonry lining 
consists of concrete walls and brick arches. The tunnels under 
Central Park and under Broadway being driven through a similar 
rock, the same method of excavation and the same manner of 
lining was used. 

The tunnel under the Harlem River was driven through soft 
ground; and it was constructed as a submarine tunnel, according 
to the caisson process. The tunnels were lined with iron made 



OPEN-CUT TUNNELING METHODS 



215 



up of segments, with radial and circumferential flanges. Con- 
crete was placed inside and flush with the flanges. 

The tracks, both in the subway and tunnels, are an intimate 
part of the concrete flooring. The rail rests on a continuous 
bearing of wooden blocks, laid with the grain running transversely 
with respect to the line of the rail, and held in place by two 
channel iron guard rails. The guard rails are bolted to metal 
cross-ties embedded in the concrete. 

Viaduct. — A considerable portion of the double-track branch 
lines north of 103d St. is viaduct, or elevated structure. The 




Fig. 121. — Harlem River Tunnel, New York Rapid Transit Railway. 

viaduct construction on the West Side Line extends, including 
approaches, from 122d St. to very near 135th St. Of this dis- 
tance, 2018 ft. 8 ins. are viaduct proper, consisting of plate 
girder spans carried by trestle bents at the ends, and by trestle 
towers for the central portion. The columns of the bents and 
towers are built-up bulb-angle and plate columns of H-section 
of the same form as those used in the bents inside the subway. 
The approaches proper are built of masonry. The elevated line 
proper consists of plate girder spans, supported on plate cross 
girders carried by columns. 



216 TUNNELING 

Stations. — Many stations are built along the line. These 
are located on each side of the street. The entrances at the 
stations consist of iron framework, with glass roofs covering the 
descending stairways. The passageways leading down are walled 
with w^hite enameled bricks and wainscoted with slabs of marble. 
The stations for the local trains are located on each side of the 
road close to the walls, since the outside tracks are reserved for 
the local trains, w^hile the middle ones are reserved for the ex- 
presses. The few stations for the express trains are located 
between the middle and outside tracks. Stations are provided 
with all the conveniences required, having toilet rooms, news 
stands, benches, etc., and are lighted day and night by numerous 
arc lamps. 

General. — The contractor completed the work in four years. 
No difficulty was encountered in doing this, since the great 
extension of the road and the great width of the avenues under 
which it runs allowed work all along the line at the same time. 
The work, briefly summarized, comprises the following items : — 

Length of all sections, ft 109,570 

Total excavation of earth, cu. yds 1,700,228 

Earth to be filled back, cu. yds 773,093 

Rock excavated, cu. yds 921,128 

Rock tunneled, cu. yds 368,606 

Steel used in structure, tons 65,044 

Cast iron used, tons 7,901 

Concrete, cu. yds 489,122 

Brick, cu. yds 18,519 

Waterproofing, sq. yds. 775,795 

Vault lights, sq. yds 6,640 

Local stations, number 43 

Express stations, number 5 

Station elevators, number 10 

Track total, Un. ft 305,380 

" underground, lin. ft 245,514 

" elevated, fin. ft 59,766 

In addition to the construction of the railway itself, it was 
necessarv to construct or reconstruct certain sewers, and to 



OPEN-CUT TUNNELING METHODS 217 

adjust, readjust, and maintain street railway lines, water pipes, 
subways, and other surface and subsurface structures, and to 
relay street pavements. 

The total cost of the work, according to the contract signed 
by Mr. McDonald, was 135,000,000. Dividing this amount by 
the total length of the road, which is 109,570 lineal feet, we have 
the unit cost a lineal foot $315, or a little less than unit of cost 
of the Boston Subway, which was 1342 per lineal foot. 

The road belongs to the city. The contractor acts as an 
agent for the city in carrying out the work, and he is the leaser 
of the road for fifty years. The work was paid for as soon as the 
various parts of the road were completed, and the money was 
obtained from an issue of city bonds. During the fifty years' 
lease the contractor will pay the interest plus 1% of the face 
value of the bonds. This 1% goes to the sinking-fund, which 
within the fifty years at compound interest forms the total sum 
required for the redemption of bonds. 

This first New York Subway has been extended to Brooklyn, 
and more lines will be built so as to form a complete underground 
railway system to accommodate the ever-increasing traveling 
crowd of the American metropolis. No new method of con- 
struction has been devised yet. The only variation from the 
illustrated methods has been where the subway is built under- 
neath the Elevated Road which had to be strongly supported 
during the construction of the subway. This has been done 
in two different ways, either by supporting the columns of 
the Elevated Road by means of two wooden A-frames abutting 
at the top and leaving a large space close to the foot of the 
column where a pit was excavated to the required depth of 
the subway, or by attaching the columns to long iron girders 
placed longitudinally and resting with both ends in firm soil. 



218 TUNNELING 



CHAPTER XVII, 

SUBMARINE TUNNELING: GENERAL DISCUS- 
SIGN. — THE SEVERN TUNNEL. 



GENERAL DISCUSSION. 

Submarine tunnels, or tunnels excavated under the beds of 
rivers, lakes, etc., have been constructed in large numbers 
during the last quarter of a century, and the projects for such 
tunnels, which have not yet been carried to completion, are 
still more numerous. Among the more notable completed 
works of this character may be noted the tunnel under the 
River Severn and those under the River Thames in England, 
the one under the River Seine in France, those under the 
St. Clair, Detroit, Hudson, Harlem and East Rivers, and the 
one under the Boston Harbor for railways, that under the East 
River for gas mains, that under Dorchester Bay, Boston, for 
sewage, and those under Lakes Michigan and Erie for the water 
supply of Milwaukee, Chicago, Buffalo, and Cleveland in America. 
For the details of the various projected submarine tunnels of 
note, which include tunnels under the English and Irish Chan- 
nels, under the Straits of Gibraltar, under the sound between 
Copenhagen in Denmark and Malino in Sweden, under the 
Messina Straits between Italy and Sicily, and under the Straits 
of Northumberland between New Brunswick and Prince Edward 
Island, and those connecting the various islands of the Straits 
of Behring, the reader is referred to the periodical literature of 
the last few years. 

Previous to attempting the driving of a submarine tunnel 
it is necessary to ascertain the character of the material it will 



SUBMARINE TUNNELING 219 

penetrate. This fact is generally determined by making dia- 
mond-drill borings along the line, and the object of ascertaining 
it is to determine the method of excavation to be adopted. If 
the material is permeable and the tunnel must pass at a small 
depth below the river bed, a method will have to be adopted 
which provides for handling the difficulty of inflowing water. 
If, on the other hand, the tunnel passes through impermeable 
material at a great depth, there will be no unusual trouble 
from water, and almost any of the ordinary methods of tun- 
neling such materials may be employed. Shallow submarine 
tunnels through permeable material are usually driven by the 
shield method or by the compressed air method, or by a method 
which is a combination of the first and second. 

It is not an uncommon experience for a submarine tun- 
nel to start out in firm soil and unexpectedly to find that this 
material becomes soft and treacherous as the work proceeds, 
or that it is intersected by strata of soft material. The method 
of deaUng with this condition will vary with the cir- 
cumstances, but generally if any considerable amount of soft 
material has to be penetrated, or if the inflow of water is very 
large, the firm-ground system of work is changed to one 
of the methods employed for excavating soft-ground sub- 
marine tunnels. The Milwaukee water supply tunnel, de- 
scribed elsewhere, is a notable example of submarine tunnels, 
began in firm material which unexpectedly developed a treacher- 
ous character after the work had proceeded some distance. 
Occasionally the task of building a submarine tunnel in the 
river bed arises. In such cases the tunnel is usually built by 
means of cofferdams in shaUow water, and by means of caissons 
in deep water. 

Submarine tunnels under rivers are usually built with a de- 
scending grade from each end which terminates in a level middle 
position, the longitudinal profile of the tunnel corresponding to 
the transverse profile of the river bottom. Where, however, 
such tunnels pass under the water with one end submerged, and 



220 TUNNELING 

the other end rising to land like the water supply tunnels of 
Chicago, Milwaukee, and Cleveland, the longitudinal profile is 
commonly level, or else descends from the shore to a level 
position reaching out under the water. 

The drainage of submarine tunnels during construction is 
one of the most serious problems with which the engineer has 
to deal in such works. This arises from the fact that, since the 
entrances of the tunnel are higher than the other parts, all of 
the seepage water remains in the tunnel unless pumped out, and 
from the possibility of encountering faults or permeable strata, 
which reach to the stream bed and give access to water in 
greater or less quantities. Generally, therefore, the excavation 
is conducted in such a manner that the inflowing water is led 
directly to sumps. To drain these sumps pumping stations 
are necessary at the shore shafts, and they should have ample 
capacity to handle the ordinary amount of seepage, and enough 
surplus capacity to meet probable increases in the inflow. For 
extraordinary emergencies this plant may have to be greatly 
enlarged, but it is not usual to provide for these at the outset 
imless their likelihood is obvious from the start. The character 
and size of the pumping plants used in constructing a number 
of well-known tunnels are described in Chapter XII. 

In this book submarine tunnels will be classified as follows : 
(1) Tunnels in rock or very compact soils, which are driven by 
any of the ordinary methods of tunneling similar materials on 
land; (2) tunnels in loose soils, which may be driven, (<x) by 
compressed air, (5) by shields, or (c) by shields and compressed 
air combined; (3) tunnels on the river bed, which are con- 
structed, (a) by cofferdams, or (b) by caissons. To illustrate 
tunnels of the first class, the River Severn tunnel in England 
has been selected; to illustrate those of the second class, the 
several tunnels discussed in the chapter on the shield system of 
tunneling and the Milwaukee tunnel is sufficient; to illustrate 
those of the third class, the Van Buren Street tunnel in Chicago, 
the Harlem, the Seine and the Detroit River tunnels are selected. 



SUBMARINE TUNNELING 221 

THE SEVERN TUNNEL. 

The Severn tunnel, which carries the Great Western Rail- 
way of England, beneath the estuary of a large river, is 4 miles 
642 yards long. It penetrates strata of conglomerate, limestone, 
carboniferous beds, marl, gravel, and sand at a minimum depth 
of 44| ft. below the deepest portion of the estuary bed. The 
following description of the work is abstracted from a paper by 
Mr. L. F. Vernon-Harcourt.* 

The first work was the sinking of a shaft, 15 ft. in diameter^ 
lined with brickwork, on the Monmouthshire bank of the Severn, 
200 ft. deep. After the Monmouthshire shaft had been sunk, a. 
heading 7 ft. square was driven under the river, rising with a 
gradient of 1 in 500 from the shaft on the Monmouthshire shore, 
so as to drain the lowest part of the tunnel. Near to the first, a 
second shaft was sunk and tubbed with iron, in which the pumps 
were placed for removing the water from the tunnel works, 
connection being made by a cross-heading with the heading 
from the first shaft. There was also a shaft on the Gloucester- 
shire shore; and two shafts inland from the first on the Mon- 
mouthshire side, to expedite the construction of the tunnel. 
Headings were then driven in both directions along the line 
of the tunnel, from the four shafts; and the drainage head- 
ing from the old shaft was continued, in the line of the tunnel, 
under the deep channel of the estuary, and up the ascending 
gradient towards the Gloucestershire shore, till, in October, 
1879, it had reached to within about 130 yards of the end of 
the descending heading from the Gloucestershire shaft. During 
this period, though the work had progressed slowly, no large 
quantity of water had been met with in any of the headings, in 
spite of their already extending under almost the whole width 
of the estuary. On October 18, 1889, however, a great spring 
was tapped by the beading which was being driven landwards 
from the old shaft, about 40 ft. above the level of the drainage 

• Proceedings Inst. G. E., vol. cxxi. 



i222 TUNNELING 

heading; and the water poured out from this land spring in 
such quantity that, flowing along the heading, falling down the 
old shaft, and thus finding its way into the drainage heading 
and the long heading of the tunnel under the estuary in con- 
nection with it, it flooded the whole of the workings in com- 
munication with the old shaft, which it also filled within twenty- 
four hours from the piercing of the spring. 

To obtain increased security against any influx of water from 
the deep channel of the estuary into the tunnel, the proposed 
level portion of the tunnel, rather more than a furlong long under 
this part, was lowered 15 ft. by increasing the descending gradient 
on the Monmouthshire side from 1 in 100 to 1 in 90, and lowering 
the proposed rail level on the Gloucestershire side 15 ft. through- 
out the ascent, so as not to increase the gradient of 1 in 100 against 
the load. A new shaft, 18 ft. in diameter, was sunk slightly 
nearer the estuary on the Monmouthshire shore than the old one; 
two shafts also were sunk on the land side of the great spring for 
pumping purposes; and additional pumping machinery was 
erected. The flow from the spring into the old shaft was ar- 
rested by a shield of oak fixed across the heading; and at last, 
after numerous failures and breakdowns of the pumps, the 
headings were cleared of water, after a diver, supplied with 
a knapsack of compressed oxygen, had closed a door in the 
long heading under the estuary; and the works w^ere resumed 
nearly fourteen months after the flooding occurred. The great 
spring was then shut off from the workings by a wall across 
the heading leading to the old shaft; and, owing to the lower- 
ing of the level of the tunnel, a new drainage heading had to 
be driven from the bottom of the new shaft at a lower level, 
which was made 5 ft. in diameter, and lined with brickwork, 
whilst the old drainage heading was enlarged to 9 ft. in diam- 
eter, and lined with brickwork, so as to aid in the permanent 
ventilation of the tunnel. The lowering of the level, moreover, 
converted the bottom tunnel headings into top headings, so 
that along more than a mile of the tunnel the semicircular arch, 



SUBMARINE TUNNELING 223 

26 ft. in diameter, was built first, and then, after lowering the 
headings, the invert was laid and the side walls were built up. 
Bottom headings were driven along the remainder of the tunnel, 
and the work was expedited by means of break-ups. Ventila- 
tion was effected in the works by a fan 18 inches in diameter 
and 7 ft. wide, fixed at the top of the new deep shaft; the rock 
was bored by drills worked by compressed air; the blasting was 
eventually effected exclusively by tonite, owing to its being 
freer from deleterious fumes than any other explosive; and the 
workings were lighted by Swan and Brush electric lamps. The 
tunnel is lined throughout with vitrified brickwork, between 
21 ft. to 3 ft. thick, set in cement, and has an invert IJ ft. to 
3 ft. in thickness; the lining was commenced towards the end 
of 1880, the headings under the river were joined in September, 
1881, and the last length of the tunnel, across the line of the great 
spring, was completed in April, 1885. 

Water came in from the river through a hole in a pool of 
the estuary, close to the Gloucestershire shore, in April, 1881, 
during the lining of a portion of the tunnel, but fortunately 
before the headings were joined. This influx was stopped by 
allowing the water to rise in the tunnel to tide-level, to prevent 
the enlargement of the hole, which was then filled up at low 
water with clay, weighted on the top with clay in bags. The 
great spring broke out again in October, 1883, and flooded the 
works a second time ; but within four weeks the water had been 
pumped out and the spring again imprisoned. During this period 
an exceptionally high tide, raised still higher by a southwesterly 
gale, inundated the low-lying land on the Monmouthshire side 
of the estuary, and, flowing down one of the inland shafts, flooded 
a section of the tunnel, but the pumps removed this water within 
a week. 

In order to construct the portion of tunnel traversing the 
line of the great spring, the water was diverted into a side head- 
ing below the level of the tunnel, leading to the old shaft, whence 
it was pumped, and the fissure below the tunnel was filled with 



224 TUNNELING 

concrete, over which the invert was built. An attempt to 
imprison the spring, on the completion of this length of tunnel, 
having resulted in imposing an excessive pressure on the brick- 
work, leading to fractures and leakage, a shaft, 29 ft. in diameter, 
was sunk at the side of the tunnel at this point in 1886, and 
pumps were erected powerful enough to deal with the entire 
flow of the spring. 

The tunnel was opened for traffic in December, 1886, and 
gives access to a double line of railway, connecting the lines 
converging to Bristol with the South Wales railway and the 
western lines. The pumping power provided at the shaft con- 
nected with the great spring, and at four other shafts, is capable 
of raising 66,000,000 gallons of water per day, the maximum 
amount pumped from the tunnel being 30,000,000 gallons a 
day. The ventilation of the tunnel is effected by fans placed 
in the two main shafts on each bank of the estuary, and the fan 
in the Monmouthshire shaft is 40 ft. in diameter, and 12 ft. wide. 
The tunnel gives passage to a large traffic, numerous through- 
trains between the north and southwest of England making 
use of it. 



SUBMARINE TUNNELING 225 



CHAPTER XVIII. 

SUBMARINE TUNNELING (Continued); THE COM- 
PRESSED AIR METHOD. — THE MILWAUKEE 
WATER-WORKS TUNNEL. 



Tunnels excavated at shallow depth from the bed of the 
river are liable to cave in under the great weight of the water 
and material above the roof. Besides, the progress of the work 
will be greatly interfered with by the water which may reach the 
tunnel passing through the loose soil in large quantities. To 
contend with these two sources of trouble, different methods of 
constructing subaqueous tunnels have been devised; they are: 
by compressed air, by shield, and finally by a combination of 
these two methods, viz., by shield and compressed air. 

The compressed air method was suggested by Mr. Haskin, 
the promoter and the first builder of the Hudson River tunnel. 
In 1874, when he began to sink the shaft for the construction of 
his tunnel, several subaqueous tunnels had already been driven 
by means of shields. Mr. Haskin had ideas of his own, and 
thought he could dispense with the shield and could trust to 
compressed air, since he was firmly convinced that compressed 
air alone could expel the water and temporarily support the 
roof of the excavation prior to the building of the lining masonry. 
In other words, he expected to substitute a core of compressed 
air for the core of earth removed. In the patent granted him for 
this method of tunneling, he expresses himself as follows: '' The 
distinguishing feature of my system is that, instead of using 
temporary facings of timber or other rigid material, I rely upon 
the air pressure to resist the caving in of the wall and infiltra- 
tion of water until the masonry wall is completed. The pressure 



90 



2G TUNNELING 

is, of course, to be regulated by the exigencies of the occasion. 
The effect of such a pressure has been found to drive water in 
from the surface of the excavation, so that the sand becomes dry." 
The compressed air method was soon found to be inefficient, 
even in the construction of the Hudson tunnel where the roof 
of the excavation was supported by timbering in the manner 
indicated in the pilot system. Thus large subaqueous railway 
tunnels cannot be driven exclusively by the compressed air 
method; still it has been successfully employed in the construc- 
tion of small tunnels driven for aqueduct purposes. But the 
use of compressed air marked a great progress in the art of 
submarine tunneling. 

THE MILWAUKEE WATER-WORKS TUNNEL. 

The following description of the Milwaukee Water- Works 
Tunnel is an example of subaqueous tunnels driven through 
good soil in the usual manner employed in land tunnels; but 
afterward when treacherous material was encountered, the work 
was continued by means of compressed air. 

The new water supply intake tunnel for the city of Milwaukee, 
Wis., is one of the most difficult examples of tunnel construction 
which American engineering practice has afforded. The diffi- 
culties were in a large measure unexpected when the work was 
decided upon and put under way. The tunnel began and ended 
in a hard, impervious clay, practically a rock, and all the pre- 
liminary investigations led to the conclusion that the same favor- 
able material would be encountered for its entire length. With 
such material a brick-lined tunnel 7J ft. in diameter presented no 
unusual problems; but after about 1640 ft. had been excavated 
from the shore end the tunnel ran out of the hard clay, and for 
the next 600 ft. or more a variety of water-bearing material was 
encountered, which tried the skill and patience of the engineer 
to their utmost. Other difficulties were indeed met with, but 
these were of minor importance in comparison with that of safely 
and successfully penetrating the water-bearing drift. 



SUBMARINE TUNNELING 227 

The work of sinking the shore shafts and excavating the 
first 1600 ft. of tunnel did not prove especially difficult. A 
hard, compact, and rock-like clay, bearing very little moisture, 
was encountered all along, and was blasted and removed in the 
ordinary manner. The only mishap which occurred with this 
portion of the work was the destruction of the contractor's 
boiler plant by fire on Jan. 12, 1891, which allowed the tunnel 
to fill with water, and delayed work about a month. By Oct. 21, 
1891, 1640 ft. had been driven, averaging about 6f ft. per day, 
all in the hard clay. No timbering had been necessary, and 
except for the first 100 ft. of the tunnel there was very little 
seepage. On the afternoon of Oct. 21 water was observed 
coming put from one of the drill holes in the heading, but no 
attention was paid to it. Shortly after a blast was fired, and 
was immediately followed by a rush of water from the heading. 
An unsuccessful attempt was made to check the flow, and the 
pumps were started; but they were unable to keep the water 
down, and after seven hours' hard work the tunnel was aban- 
doned. By the next morning the tunnel and shaft were full of 
water. 

Several attempts were made to empty the tunnel; but the 
limited pumping capacity was not equal to the task, and it was 
finally decided to install larger pumps. The pumping had, how- 
ever, shown that about 1000 gallons of water a minute was 
coming through the leak. With the increased pumping plant 
the tunnel was finally laid dry Feb. 13, 1892. Upon examina- 
tion the head of the drift was found to be in the same undis- 
turbed condition in which it was left when the water broke in 
three months before. 

A brick bulkhead was built into the end of the brickwork 
of the tunnel, and provided with a timber door for passage, and 
two 10-in. pipes for the outlet of the water. With these open- 
ings closed, the flow was checked sufficiently to allow the placing 
of pumps at the bottom of the shore shaft. Meanwhile the 
pressure of the water against the bulkhead caused dangerous 



228 TUNNELING 

leakage, and so after the pumps were in position the 10-in. pipes 
were opened, relieving the pressure and allowing the water its 
normal rate of flow. Trouble with the pumps now arose, and 
after various stoppages and breaks the discharge pipe finally 
fell, disabling the whole plant. It became necessary to close 
the 10-in. pipes in the bulkhead and draw up the pumps. This 
allowed the tunnel to again fill with water. 

After thoroughly overhauling the pumping machinery, the 
contractor again laid the tunnel dry on March 19; and after 
the pumps had been permanently placed so as to take care of 
the water, an examination of the work was made. It was found 
that the water was coming from the north, and with the hope 
of avoiding the difficulties of the old heading, it was decided to 
make a detour of the south. On April 16 work was begun at 
a point about 90 ft. back from the face, and deflecting the line 
about 38° toward the south. About 38 ft. from the angle of 
junction a brick bulkhead with two 8-in. openings was built 
into the new bore. The work progressed successfully for about 
75 ft., when water was again encountered; and upon pushing 
forward the heading, gravel and sand came in such quantities 
that it was found impracticable to continue the work further. 
On June 1 the bulkhead was permanently closed, and the work 
in this direction was abandoned. 

A further and closer examination was now made of the head- 
ing first abandoned. Upon breaking through the rock-like 
clay it was found that the water came from an underground 
stream flowing from the north through a well defined channel 
in red clay. This channel was about 13 ft. above the grade of 
the tunnel; and above it in every direction visible was a bed of 
hard, dry, red clay, while immediately in front of the face of the 
work was a bank of coarse gravel Fig. 122 is a sketch of the 
channel and stream where they entered the work. In this last 
drawing the photograph has been followed exactly, no particu- 
lar being exaggerated in the slightest. The water from this 
stream was clear and pure; and a chemical analysis showed 



SUBMARINE TUNNELING 



229 



that it was not lake water, but must come from some separate 
source. 

While the engineer did not consider the difficulty of pro- 
ceeding along the old line insurmountable, it was decided to be 
less difficult on the whole to go back from 150 ft. to 175 ft. and 
deflect the line to the north and upward, so as to pass over the 
underground entrance. Instead of allowing the water to flow 
at its normal rate and take care of it by pumping, the contrac- 




Encj.news., 

Fig. 122. — Sketch Showing Underground Stream, Milwaukee Water-Works Tunnel. 



tors desired to reduce the pumping, and to this end they con- 
structed a bulkhead just west of the deflection toward the 
south with a view of shutting off the water. The water, how- 
ever, accumulated with a pressure of some 50 lbs. per sq. in. 
and penetrated the filling around the brick lining of the tunnel, 
preventing the cutting through of the lining for the new line. 
A second bulkhead was then built about 20 ft. west of the first, 
but with not much better results, for upon closing it the water 
was found to leak through the brickwork for a long distance 



230 TUNNELING 

west. Finally on Aug. 2, 1892, the contractors lifted their 
pumps and allowed the tunnel to fill again with water. 

No further work was done on the tunnel by the contractors, 
although they continued work on the lake shaft for some months. 
Difficulties had, however, arisen here, which will be described 
further on; and finally a disagreement arose between the con- 
tractors and the city over the delay in prosecuting the tunnel 
work and over one or two other questions, which resulted in the 
Gity Council suspending their contract and ordering the Board 
of Public Works to go ahead with the work. 

The first step to be taken by the engineer was to purchase 
adequate pumping machinery and empty the tunnel. This was 
effected Jan. 17, 1894; and as soon as practicable thereafter the 
two bulkheads were removed and the tunnel cleaned, tram-car 
tracks laid, and ^everything prepared for work. It was now 
determined to go ahead on the original line of the tunnel if 
possible, and the bulkhead here was removed and work begun. 
Meanwhile, a safety bulkhead had been built to replace the first 
one torn away. This was provided with a door and drain- 
age pipes. Work was begun on the original heading, but had 
proceeded only a little way when the water broke in, driving 
out the workmen. This was removed three or four times, when 
the flow suddenly increased to 3000 gallons per minute. An 
examination of the lake bottom above the break showed that it 
had settled down, indicating that the new break connected with 
the lake bottom, and making further work along the original 
line out of the question. 

The question now arose what it was best to do. It was 
impracticable to use a shield, as the material ahead of the break 
required blasting, and the pressure from above was enormous. 
On account of its expense and difficulty of application the 
freezing process did not seem advisable, and the plenum process 
was likewise out of the question on account of the great pressure 
which would be required at this depth. The detour to the 
south which had been made by the contractor had been unsuc- 



SUBMARINE TUNNELING 231 

cessful, and had left the ground in a treacherous condition. 
To depress the tunnel was not advisable, for it was not by any 
means certain that the bed of gravel could be avoided in that 
way; and, moreover, it would be necessary to ascend again 
further on, and thus leave a trap which would effectually cut 
off escape to those at work on the face if water again broke into 
the tunnel. 

It was finally decided that the old plan of deflecting the 
line toward the north and upward so as to pass over the under- 
ground stream should be tried. A hole was therefore cut through 
the tunnel lining 1433 ft. from the shore, and work was begun 
on a detour of 20° toward the north and an upward grade of 
10%. Fair progress was made on this new line, gradually 
ascending into solid rock, until May 10, when the test borings, 
which were constantly made in every direction from the face, 
showed that sand was being approached. A brick bulkhead 
was therefore built into the masonry as a safeguard, should it 
happen that water was encountered in large quantities. As the 
borings seemed to indicate that the top surface of the rock under- 
lying the sand was nearly level, the lower half of the tunnel was 
first excavated, leaving about 18 ins. of the rock to serve as a 
roof (Sketch a. Fig. 123), and the brick invert was built for 
a distance of 52 ft. The rock roof was then carefully broken 
through for short distances at a time, and short sheeting driven 
ahead into the sand, which proved to be a very fine quicksand 
flowing through the smallest openings. Extreme care had to be 
taken in this work, but little by little the brickwork was pushed 
ahead until at a distance of 90 ft. from the point where the sand 
was first met, and 208 ft. from the old tunnel, the sand stopped 
and the heading entered a hard clay. 

All this work had been done on an ascending grade, and the 
ascent was continued about 40 ft. farther in the clay. By this 
time a sufficient elevation was gained to pass over the under- 
ground stream, and the tunnel line was changed to head toward 
the lake shaft, and the grade reduced to a level. The under- 



232 



TUNNELING 



ground stream was passed without trouble and the tunnel con- 
tinued for a distance of 54 ft. without difficulty. On July 
10 the clay in the heading suddenly softened, and before the 
miners could secure it by bracing, the water rushed in, followed 
by gravel, filling up solidly some 34 ft. of the tunnel before it 
was stopped by a timber bulkhead hastily built. 




Longitudinal Section Showing Method of 
Construction in Rock Covered with Quicksand. 

Sketch "a". 



'SM^M'lfrM^M^^'^^^^ ^-' 









^^^ 



Section A-B-C-D. 
Sketch "c". 




'o[Boulcler5 



H?A fa-' *' 

Longitudinal Section Cff Tunnel 

Sketch "b". 




Fig. 123. 



Cross Section Showing Manner of 
Constructing Lining around Boulder. 

Sketch 'd." 

Sketch Showing Methods of Lining, Milwaukee Water- Works Tunnel. 



Upon examining the lake bottom a cavity over 60 ft. deep and 
10 ft. in diameter was found directly over the end of the tunnel, 
which had been caused by the gravel breaking into the tunnel. 
Having now reached an elevation where it was possible to use 
compressed air, it was determined to put in double air-locks 
and use the plenum process. The locks were built, and some 



SUBMARINE TUNNELING 233 

670 cu. yds. of clay were dumped into the hole in the lake bottom. 
On Aug. 4 the air-locks were tried with 26 lbs. air pressure; 
but, upon a temporary release of the pressure, the water passed 
around the locks and back of the tunnel lining for some distance, 
and even forced through the lining, carrying considerable clay 
and fine sand with it. Upon sounding the lake bottom it was 
found that the cavity had again increased to a depth of 65 ft., 
whereupon an additional 600 cu. yds. of clay were dumped into it. 

On account of the water leaking through the brickwork, the 
only dry place to cut through the brickwork and build in an 
air-lock was just ahead of the brick bulkhead. This lock was 
completed Aug. 27, and to avoid encountering the danger of 
the direct connection with the lake at the end of the drift, it 
was decided to make another detour to the north. On Aug. 28, 
therefore, the brick on the north side of the tunnel 12 ft. back 
from the end of the brickwork was cut through under 25 lbs. 
air pressure, and work proceeded in good, hard clay. The 
original air-lock was cut out and a new lock built into this 
clay about 34 ft. from the last detour, to be used in case of 
further difficulties. After building the tunnel for about 80 ft. 
from the detour, the soundings again indicated the approach to 
gravel and water, and on Oct. 14 the water broke through from 
the bottom in such volume and with such force that the men 
ran out, closing every air-lock and the valves of every drain in 
their haste to escape, until the brick bulkhead was reached. 
It was with great difficulty that the portion of the tunnel up to 
the last air-lock was recovered and cleaned out. 

It was now recognized that a pressure of from 38 to 40 lbs. 
of air would be needed to hold this water, and accordingly an- 
other compressor was added to the plant. With a pressure of 
36 lbs. the water was driven out and the work again started. 
At this time also an additional 350 cu. yds. of clay were dumped 
into the hole in the lake bottom. Altogether, 1620 cu. yds. of 
clay had been put into this hole. 

Loose gravel and boulders, some of immense size, were now 



234 TUNNELING 

encountered, and the work became exceedingly difficult on 
account of the great escape of air. The interstices between the 
gravel and boulders were not filled with silt or sand, but con- 
tained water. Moreover, this material extended upward to the 
lake bottom, as was shown by the escape of air at the surface of 
the lake. For an area of several hundred square feet the surface 
of the water resembled a pot of boiling water. At times the 
air would escape very rapidly; and again only a few bubbles 
would show. 

It need hardly be said that the work in this gravel was very 
slow. It was impossible to blast or to tear out the large boulders 
whole, as so much surface would be exposed that an inrush of 
water would take place despite the air pressure. The method 
of procedure was to excavate a heading and build the brick roof 
arch first,' and then to take out the bench and build the in- 
vert. Fig. 123 gives a number of sketches showing how the 
work was done. A short piece of heading was taken out, the 
top and face of the bench being meanwhile plastered with clay 
(Sketches h and c, Fig. 123) to reduce the escape of air, and 
then the roof arch was built and supported on side sills resting 
on the bench. Bit by bit the roof arch was pushed forward 
until some little distance had been completed, then the heading 
was plastered with clay and the bench taken out little by little 
and the invert built. All the gravel except the small area 
upon which work was actually in progress was kept thoroughly 
plastered with clay; and as the air escaped through the com- 
pleted brickwork very rapidly, water was allowed to cover a 
portion of the invert (see Sketch c, Fig. 123), so as to reduce 
the area of escape. 

When a large boulder was reached, which lay partly within 
and partly without the tunnel section, the lining was built out 
and around it, as shown in Sketch d, Fig. 123. The boulder 
was then broken and taken out. All through this gravel bed 
the cross-section of the lining is made irregular by the con- 
struction of these pockets in the lining to get around boulders. 



SUBMARINE TUNNELING 235 

Sometimes they were on one side and sometimes on the other, 
or on both, or at the top or bottom. In fact, there was no 
regularity. Despite the hazard and danger of this work, con- 
tinual progress was made, though sometimes it was only 4 ft. 
of completed tunnel per week, w^orking night and day; and, if 
some cases of caisson disease be excepted, the only mishap oc- 
curring was a fire which got into the timber packing behind 
the lining and caused some trouble. From the gravel the tunnel 
ran into clay and quicksand, and then into hard, dry clay similar 
to that encountered near the shore. Some difficulty was had 
with the quicksand, but it was successfully overcome; and when 
the hard clay was struck, the trouble, as far as the work from 
the shore shaft was concerned, was virtually over. 

Meanwhile, a different set of afflictions had come upon the 
engineer and contractors in sinking the lake shaft and driving 
the heading toward shore. This shaft was intended to be 
built by sinking a cast-iron cylinder 10 ft. in diameter, made 
up of sections bolted together. Work was begun July 5, 1892, 
and the sinking was accomplished first by weighting the cylinder, 
and afterwards by pumping out the sand and water within it 
until the pressure from the outside broke through under the 
cutting edge and forced the sand into the cylinder, allowing it 
to sink a little. From 10 to 30 cu. yds. of sand were carried 
into the cylinder each time, and finally it was feared that if 
the process continued, the crib, which had been previously 
erected, would be undermined. On Sept. 6, therefore, the 
contractors were ordered to discontinue this method of work. 
No change was made, however, until Oct. 1, when the cylinder 
had reached a depth of 68 ft., and by this time there was quite 
a large cavity underneath the crib. This was refilled, and the 
cylinder pumped out, and excavation begun inside of it. On 
Oct. 11 a 2i-ft. deep ring of brickwork was laid underneath 
the cutting edge; but in trying to put in another ring beneath 
the first, two days later, the sand and water broke through the 
bottom, driving the men out, and filling the cylinder to a depth 



236 TUNNELING 

of 16 ft. with sand. The pumps were started, but the water 
could not be lowered to a greater depth than 60 ft. 

At the request of the contractors, the city engineer had a 
boring made at the center of the shaft to determine the char- 
acter of the material to be further penetrated. This boring 
showed that sand mixed with loam and gravel would be found 
for a depth of 26 ft., then would come 15 ft. of red clay, and 
finally a layer of hard clay like that penetrated by the shore 
end of the tunnel. About the middle of December the con- 
tractors made another attempt to pump the shaft, but find- 
ing that the water came in at the rate of 25 gallons a minute, 
abandoned the attempt. In the latter part of February prepa- 
rations were made to put an air-lock in the shaft and use com- 
pressed air. Hardly had the work been begun by this system 
when, on- April 20, 1893, a terrific easterly storm swept the top 
of the crib bare of the buildings and machinery, and drowned 
all but one of the 15 men at work there. 

This disaster delayed the work for some time, but in June 
the contractors erected a new building and new machinery, and 
resumed work. Very little progress was made; and the air es- 
caped so rapidly that it loosened the sand surrounding the 
shaft and reduced the friction to such an extent that on July 
28 the entire cylinder lifted bodily about 6 ft., and sand rushed 
in, fining the lower part of the cylinder to within 45 ft. of the 
lake surface. No further work was done by the contractors 
although they submitted a proposition to sink a steel cylinder 
inside the cast-iron cylinder and extending from 5 ft. above 
datum to 100 ft. below datum for $300 per ft. This proposi- 
tion was refused by the city; and since work on the tunnel 
proper had been abandoned by the contractors some time before, 
as had already been described, the city suspended their contract 
on Oct. 19. 

On Oct. 30 a contract was made with Mr. Thos. Murphy 
of Milwaukee, Wis., to sink a steel cylinder inside the old iron 
cylinder. The water was first pumped out of the old cylinder, 



SUBMARINE TUNNELING 237 

and a timber bulkhead built at the bottom. On this the steel 
cylinder was built, and then the bulkhead was removed. Air 
pressure was put on, and the excavation proceeded successfully 
until the bottom layer of clay was met with, when all chances 
for trouble ceased. 

The cylinder, as it was completed, penetrated 9 ft. into the 
hard clay, and was underpinned with brickwork for a depth of 
29 ft. or more, to a point 4 ft. below the grade line of the tunnel. 
At the lower end, the section of the shaft was changed from a 
circle to a square. Later the steel cylinder was lined with brick. 

On March 28, 1894, an agreement was made with Mr. Thos. 
Murphy to construct the tunnel from the lake shaft toward 
the shore. Except that considerable water was encountered, 
which, owing to inadequate pumping machinery, filled the 
tunnel and shaft at two different times, and had to be removed, 
no very great difficulty was had with this part of the work. 

On July 28, 1895, the headings from the lake and shore shafts 
met. Meanwhile the cast-iron pipe intake, the intake crib, etc., 
had been completed, and practically all that remained to be 
done was to clean the tunnel and lift the pumping machinery 
at the shore shaft. During the cleaning, the air pressure had 
been kept up on account of the leakage through the brick lining, 
and, indeed, the pressure "was kept up until the last possible 
moment, and everything made ready for removing the air-locks, 
bulkheads, pumps, etc., in the least possible time. The pumps 
were the last to come out. 



238 TUNNELING 



CHAPTER XIX. 
SUBMARINE TUNNELING (Continued). 



THE SHIELD SYSTEM. 

Historical Introduction. — The invention of the shield system 
of tunneling through soft ground is generally accredited to Sir 
Isambard Brunei, a Frenchman born in 1769, who emigrated to 
the United States in 1793, where he remained six years, and 
then went to England, in which country his epoch-making in- 
vention in tunneling was developed and successfully employed in 
building the first Thames tunnel, and where he died in 1849, a 
few years after the completion of this great work. Sir Isambard 
is said to have obtained the idea of employing a shield to tunnel 
soft ground from observing the work of ship-worms. He no- 
ticed that this little animal had a head provided with a boring 
apparatus with which it dug its way into the wood, and that its 
body threw off a secretion which lined the hole behind it and 
rendered it impervious to water. To duplicate this operation 
by mechanical means on a large enough scale to make it ap- 
plicable to the construction of tunnels was the plan which 
occurred to the engineer; and how closely he followed his ani- 
mate model may be seen by examining the drawings of his 
first shield, for which he secured a patent in 1818. Briefly 
described, this device consisted of an iron cylinder having at 
its front end an auger-like cutter, whose revolution was in- 
tended to shove away the material ahead and thus advance the 
cylinder. As the cylinder advanced the perimeter of the hole 
behind was to be lined with a spiral sheet-iron plating, which 
was to be strengthened with an interior lining of masonry. It 



SUBMARINE TUNNELING 239 

will be seen that the mechanical resemblance of this device to 
the ship-worm, on which it is alleged to have been modeled, was 
remarkably close. 

In the same patent in which Sir Isambard secured protection 
for his mechanical ship-worm he claimed equal rights of inven- 
tion for another shield, which is of far greater importance in 
being the prototype of the shield actually employed by him in 
constructing the first Thames tunnel. This alternative inven- 
tion, if it may be so termed, consisted of a group of separate 
cells which could be advanced one or more at a time or all to- 
gether. The sides of these cells were to be provided with friction 
rollers to enable them to slide easily upon each other; and it 
was also specified that the preferable motive power for advanc- 
ing the cells was hydraulic jacks. To summarize briefly, there- 
fore, the two inventions of Brunei comprehended the protecting 
cylinder or shield, the closure of the face of the excavation, 
the cellular division, the hydraulic-jack propelling power, and 
cylindrical iron lining, which are the essential characteristics 
of the modern shield system of tunneling. The next step re- 
quired was the actual proof of the practicability of Brunei's 
inventions, and this soon came. 

Those who have read the history of the first Thames tunnel 
will recall the early unsuccessful attempts at construction which 
had discouraged English engineers. Five years after Brunei's 
patent was secured a company was formed to undertake the 
task again, the plan being to use the shield system, under the 
personal direction of its inventor as chief engineer. For this 
work Brunei selected the cellular shield mentioned as an alter- 
native construction in his original patent. He also chose to 
make this shield rectangular in form. This choice is commonly 
accounted for by the fact that the strata to be penetrated by the 
tunnel were practically horizontal, and that it was assumed by 
the engineer that a rectangular shield would for some reason 
best resist the pressures which would be developed. AVhatever 
the reason may have been for the choice, the fact remains that 



240 TUNNELING 

a rectangular shield was adopted. The tunnel as designed con- 
sisted of two parallel horseshoe tunnels, 13 ft. 9 ins. wide and 
16 ft. 4 ins. high and 1200 ft. long, separated from each other 
by a wall 4 ft. thick, pierced by 64 arched openings of 4 ft. 
span, the whole being surrounded with massive brickwork built 
to a rectangular section measuring over all 38 ft. wide and 
22 ft. high. 

The first shield designed by Brunei for the work proved in- 
adequate to resist the pressures, and it was replaced by another 
somewhat larger shield of substantially the same design, but of 
improved construction. This last shield was 22 ft. 3 ins. high 
and 37 ft. 6 ins. wide. It was divided vertically into twelve 
separate cast-iron frames placed close side by side, and each 
frame was divided horizontally into three cells capable of sepa- 
rate movement, but connected by a peculiar articulated con- 
struction, which is indicated in a general way by Fig. 124. To 
close or cover the face of the excavation, poling-boards held 
in place by numerous small screw-jacks were employed. Each 
cell or each frame could be advanced independently of the 
others, the power for this operation being obtained by means 
of screw-jacks abutting against the completed masonry lining. 
Briefly described, the mode of procedure was to remove the 
poling-boards in front of the top cell of one frame, and excavate 
the material ahead for about 6 ins. This being done, the top 
cell was advanced 6 ins. by means of the screw-jacks, and the 
poling-boards were replaced. The middle cell of the frame was 
then advanced 6 ins. by repeating the same process, and finally 
the operation was duplicated for the bottom cell. With the 
advance of the bottom cell one frame had been pushed ahead 
6 ins., and by a succession of such operations the other eleven 
frames were advanced a distance of 6 ins., one after the other, 
until the whole shield occupied a position 6 ins. in advance of 
that at which work was begun. The next step was to fill the 
6-in. space behind the shield with a ring of brickwork. 

The illustration. Fig. 124, is the section parallel to the ver- 



STTBMAKINE TUNNELING 



241 



tical plane of the tunnel through the center of one of the frames, 
and it shows quite clearly the complicated details of the shield 
construction. Two features which are to be particularly noted 




Fig. 124. — Longitudinal Section of Brunei's Shield, First Thames Tunnel. 



are the suspended staging and centering for constructing the 
roof arch, and the top plate of the shield extending back and 
overlapping the roof masonry so as to close completely the 
roof of the excavation and prevent its falling. Notwithstand- 



242 



TUNNELING 



ing its complicated construction and unwieldy weight of 120 
tons, this shield worked successfully, and during several months 
the construction proceeded at the rate of 2 ft. every 24 hours. 
There were two irruptions of water and mud from the river 
during the work, but the apertures were effectually stopped by 
heaving bags of clay into the holes in the river bed, and cover- 
ing them over with tarpaulin, with a layer of gravel over all. 
The tunnel was completed in 1843, at a cost of about S5600 
per lineal yard, and 20 years from the time work was first com- 
menced, including all delays. 

The next tunnel to be built by the shield system was the 
tunnel under London Tower constructed by Barlow and Great - 

,,. . . .. head and begun in 1869. In 

1863 Mr. Peter W. Barlow se- 
cured a patent in England for 
a system of tunnel construction 
comprising the use of a circu- 
lar shield and a cylindrical cast- 
iron lining. The shield, as 
shown by Fig. 125, was simply 
an iron or steel plate cylin- 
der. The cylinder plates were 
thinned down in front to form a cutting edge, and they extended 
far enough back at the rear to enable the advance ring of the 
cast-iron lining to be set up within the cylinder. In simplicity 
of form this shield was much superior to Brunei's; but it seems 
very doubtful, since it had no diametrical bracing of any sort, 
whether it would ever have withstood the combined pressure of 
the screw-jacks and of the surrounding earth in actual opera- 
tion without serious distortion, and, probably, total collapse. 
It should also be noted that Barlow's shield made no provision 
for protecting the face of the excavation, although the inventor 
did state that if the soil made it necessary such a protection 
could be used. The patent provided for the injection of liquid 
cement behind the cast-iron lining to fill the annular space left 




Fig. 125. — First Shield Invented by Barlow. 



SUBMARINE TUNNELING 



243 



by the advancing tail-plates of the shield. Although Barlow 
made vigorous efforts to get his shield used, it was not until 
1868 that an opportunity presented itself. In the meantime 
the inventor had been studying how to improve his original 
device, and in 1868 he secured additional patents covering these 
improvements. Briefly described, they consisted in partly clos- 
ing the shield with a diaphragm as shown by Fig. 126. The 
uninclosed portion of the shield is here shown at the center, but 
the patent specified that it might also be located below the 
center in the bottom part of the shield. The idea of the con- 
struction was that in case of an irruption of water the upper 
portion of the shield could be kept open by air pressure, and 
work prosecuted in 
this open space until 
the shield had been 
driven ahead suffi- 
ciently to close the 
aperture, when the 
normal condition of 
affairs would be re- 
sumed. This was ob- 
viously an improve- 
ment of real merit. The partial diaphragm also served to 
stiffen the shield somewhat against collapse, but the thin plate 
cutting-edges and most of the other structural weaknesses were 
left unaltered. To summarize briefly the improvements due to 
Barlow's work, we have: the construction of the shield in a 
single piece; the use of compressed air and a partial diaphragm 
for keeping the upper part of the shield open in case of irrup- 
tions of water; and the injection of liquid cement to fill the 
voids behind the lining. 

Turning now to the London Tower tunnel work, it may first 
be noted that Barlow found some difficulty in finding a con- 
tractor who was willing to undertake the job, so little confidence 
had engineers generally in his shield system. One man, however. 





Longitudinal Section. Cross Section . 

Fig. 126. — Second Shield Invented by Barlow. 



244 TUNNELING 

Mr. J. H. Greathead, perceived that Barlow's device presented 
merit, although its design and construction were defective, and he 
finally undertook the work and carried it to a brilliant success. 
The tunnel was 1350 ft. long and 7 ft. in diameter, and penetrated 
compact clay. Work was begun on the first shore shaft on Feb. 
12, 1869, and the tunnel was completed the following Christmas, 
or in something short of eleven months, at a cost of £14,500. 

The shield used was Barlow's idea put into practical shape by 
Greathead. It- consisted of an iron cylinder, or, more properly, a 
frustum of a cone whose circumferential sides were very slightly 
inclined to the axis, the idea being that the friction would be less 
if the front end of the shield were slightly larger than the rear 
end. The shell of the cone was made of J-in. plates. The thinned 
plate cutting-edge of Barlow's shield was replaced by Greathead 
with a circular ring of cast iron. Greathead also altered the con- 
struction of the diaphragm by arranging the angle stiffeners so 
that they ran horizontally and vertically, and by fastening the 
diaphragm plates to an interior cast-iron ring connected to the 
shell plates. This was a decided structural improvement, but it 
was accompanied with another modification which was quite as 
decided a retrogression from Barlow's design. Greathead made 
the diaphragm opening rectangular and to extend very nearly 
from the top to the bottom of the shield, thus abandoning the 
element of safety provided by Barlow in case of an irruption 
of water. Fortunately the material penetrated by the shield 
for the Tower tunnel was so compact that no trouble was had 
from water; but the dangerous character of the construction 
was some years afterwards disastrously proven in driving the 
Yarra River tunnel at Melbourne, Australia. To drive his 
shield Greathead employed six 2J-in. screw-jacks capable of 
developing a total force of 60 tons. The tails of the jack bore 
against the completed lining, which consisted of cast-iron rings 
18 ins. wide and f in. thick, each ring being made up of a crown 
piece and three segments. The different segments and rings 
were provided with double (exterior and interior) flanges, by 



SUBMARINE TUNNELING 



245 




Fig. 127. — Shield Suggested by Greathead for the 
Proposed North and South Woolwich Subway. 



means of which they were bolted together. The soil behind 
the lining was filled with hquid cement injected through small 
holes by means of a hand 
pump. 

The remarkable suc- 
cess of the London Tower 
tunnel encouraged Bar- 
low to form in 1871 a 
company to tunnel the 
Thames between South- 
wark and the City, and 
Greathead, in 1876, to project a tunnel under the same water- 
way known as the North and South Woolwich Subway. Bar- 
low's concession was abrogated by Parliament in 1873, without 

any work having been 
done. Greathead pro- 
gressed far enough with 
his enterprise to construct 
a shield and a large 
amount of the iron lining 
when the contractors 
abandoned the work. 
From the brief descrip- 
tion of his shield given 
by Greathead to the Lon- 
don Society of Civil En- 
gineers, it contained sev- 
eral important differences 
from the shield built by 
him for the London 
Tower tunnel, as is shown 
by Fig. 127. The changes 
which deserve particular notice are the great extension of the 
shield behind the diaphragm, the curved form of the diaphragm, 
and the use of hydraulic jacks. Greathead had also designed 




->; 

Fig. 128. — Beach's Shield Used on Broadway 
Pneumatic Railway Tunnel. 



246 



TUNNELING 



for this work a special crane to be used in erecting the cast-iron 
segments of the hning. 

AVhile these works had been progressing in England, Mr. 
Beach, an American, received a patent in the United States for 
a tunnel shield of the construction shown by Fig. 128, which 
was first tried practically in constructing a short length of 
tunnel under Broadway for the nearly forgotten Broadway 
Pneumatic Underground Railway. This shield, as is indicated by 




Fig. 129. — Shield for City and South London Railway. 



the illustration, consisted of a cylinder of wood with an iron- 
cutting-edge and an iron tail-ring. Extending transversely 
across the shield at the front end were a number of horizontal 
iron plates or shelves with cutting-edges, as shown clearly by 
the drawing. The shield was moved ahead by means of a 
number of hydraulic jacks supplied with power by a hand pump 
attached to the shield. By means of suitable valves all or 
any lesser number of these jacks could be operated, and by 
thus regulating the action of the motive power the direction of 



SUBMARINE TUNNELING 



I r * ♦ t ^ 



- • • Tit: 



^Holesforp.bolrs' 







.f..-.p/:'/2'f-''3'6ff- ?-. 



..,_. SECTION SHOWING HALF OF WALL F. 



^rrr: 







-^>^SECnON SHOWING HALF OF WALL E. ^u. 




248 



TUNNELING 



the shield could be altered at will. Work was abandoned on 
the Broadway tunnel in 1870. In 1871-2 Beach's shield was 
used in building a short circular tunnel 8 ft. in diameter in 
Cincinnati, and a little later it was introduced into the Cleve- 
land water-works tunnel 8 ft. in diameter. In this latter work, 
which was through a very treacherous soil, the shield gave a 
great deal of trouble, and was finally so flattened by the pressures 
that it was abandoned. The obviously defective features of 







Longitudinal Section. Cross Section. 

Fig. 131. — Shield for Blackwall Tunnel. 

this shield were its want of vertical bracing and the lack of any 
means of closing the front in soft soil. 

With the foregoing brief review of the early development of 
the shield system of tunneling, we have arrived at a point where 
the methods of modern practice can be studied intelligently. 
In the pages which follow we shall first illustrate fully the con- 
struction of a number of shields of typical and special construc- 
tion, and follow these illustrations with a general discussion of 
present practice in the various details of shield construction. 

Mr. Raynald Legouez, in his excellent book upon the shield 
system of tunneling, considers that tunnel shields may be di- 



SUBMARINE TUNNELING 



249 




Transverse Section. 
- 7zji 




Longitudinal Section. 

Fig. 132. — Elliptical Shield for Clichy Sewer Tunnel, Paris. 

vided into three classes structurally, according to the character 
of the material which they are designed to penetrate. In the 
first class he places shields designed to work in a stiff and com- 



250 TUNNELING 

paratively stable soil, like the well-known London clay; in the 
second class are placed those constructed to work in soft clays 
and silts; and in the third class those intended for soils of an 
unstable granular nature. This classification will, in a general 
way, be kept by the writer. As a representative shield of 



Longitudi na\ Section ._> 



Cross Section. 
Fig. 133. — Semi-elliptical Shield for Clichy Sewer Tunnel. 

the first class, the one designed for the City and South London 
Railway is illustrated in Fig. 129. The shields for the London 
Tower tunnel, the AVaterloo and City Railway, the Glasgow Dis- 
trict Subway, the Siphons of Clichy and Concorde in Paris, and 
the Glasgow Port tunnel, are of the same general design and 
construction. To represent shields of the second class, the St. 



SUBMARINE TUNNELING 



251 



Clair River and Blackwall shields are shown in Figs. 130 and 
131. The shields for the Mersey River, the Hudson River, 
and the East River tunnels also belong to this class. To repre- 
sent shields of the third class, the elHptical and semi-elliptical 
shields of the Clichy tunnel work in Paris are shown by Figs. 132 




Details of Casting 
Supporting Ends of Jacks. 



Details of Casting under Ends Longitudinal Section C-Q. 

of Girders. 

Fig. 134. — Roof Shield for Boston Subway, 



and 133. The semi-circular shield of the Boston Subway is 
illustrated by Fig. 134. 

Prelini's Shield. — In closing this short review mention will 
be made of a new shield designed and patented by the Author 
and shown in Fig. 135. It is an articulated shield composed of 
two separated shields whose outer shells overlap each other. 
The shields are connected together by means of hydraulic jacks 
attached all around the two diaphragms. Between these dia- 
phragms is a large inclosed space called a safety chamber, 
where the men can withdraw in case of accidents and where the 
air can be immediately raised to the required pressure. This is 



252 TUNNELING 

an advantage in case of blow-outs, because the flooding of the 
tunnel is prevented, while the accident is Hmited to only a few 
feet from the front. On account of the shield being advanced 



Fig. 135. — Transversal and Longitudinal Section of Prelini's Shield. 

half at a time it is always under control and is thus better 
directed through grade and alignment. Besides, this shield will 
not rotate around its axis and consequently it can be built of 
any shape, thus permitting the construction of subaqueous tun- 
nels of any cross-section and even with a wider foundation, which 
is impossible to-day with the ordinary rotating shields of circu- 
lar cross-section. 

SHIELD CONSTRUCTION. 

General Form. — Tunnel shields are usually cylindrical or 
semi-cylindrical in cross-section. The cylinder may be circular, 
elliptical, or oval in section. Far the greater number of shields 
used in the past have been circular cylinders; but in one part 
of the sewer tunnel of Clichy, in Paris, an elliptical shield with 
its major axis horizontal, was used, and the German engineer, 
Herr Mackensen, has designed an oval shield, with its major 
axis vertical. A semi-elHptical shield was employed on the 
Clichy tunnel, and semi-circular shields were used on the Bal- 
timore Belt Line tunnel and the Boston Subway in America. 
Generally, also, tunnel shields are right cylinders; that is, the 



SUBMARINE TUNNELING 253 

front and rear edges are in vertical planes perpendicular to the 
axis of the cylinder. Occasionally, however, they are oblique 
cylinders; that is, the front or rear edges, or both, are in planes 
oblique to the axis of the cylinder. One of these visor-shaped 
shields was employed on the Clichy tunnel. 

The Shell. — It is absolutely necessary that the exterior sur- 
face of the shell should be smooth, and for this reason the ex- 
terior rivet heads must be countersunk. It is generally admitted, 
also, that the shell should be perfectly cylindrical, and not 
conical. The conical form has some advantage in reducing the 
frictional resistance to the advance of the shield; but this is 
generally considered to be more than counterbalanced by the 
danger of subsidence of the earth, caused by the excessive void 
which it leaves behind the iron tunnel lining. For the same 
reason the shell plate, which overlaps the forward ring of the 
lining, should be as thin as practicable, but its thickness should 
not be reduced so that it will deflect under the earth pressure 
from above. Generally the shell is made of at least two thick- 
nesses of plating, the plates being arranged so as to break joints, 
and, thus, to avoid the use of cover joints, to interrupt the 
smooth surface which is so essential, particularly on the exterior. 
The thickness of the shell required will vary with the diameter 
of the shield, and the character and strength of the diametrical 
bracing. Mr. Raynald Legouez suggests as a rule for determin- 
ing the thickness of the shell, that, to a minimum thickness of 
2 mm., should be added 1 mm. for every meter of diameter 
over 4 meters. Referring to the illustrations. Figs. 128 to 132 
inclusive, it will be noted that the St. Clair tunnel shield, 21J ft. 
in diameter, had a shell of 1-in. steel plates with cover-plate 
joints and interior angle stiff eners; the shell of the East River 
tunnel shield, 11 ft. in diameter, was made up of one J-in. and 
one f-in. plate; the Blackwall tunnel shield, 27 ft. 9 ins. in diam- 
eter, had a shell consisting of four thicknesses of |-in. plates; 
and the Clichy tunnel shield, with a diameter of 2.06 meters, 
had a shell 2 milHmeters thick. 



254 TUNNELING 

Front-End Construction. — By the front end is meant that 
portion of the shield between the cutting-edge and the vertical 
diaphragm. The length of this portion of the shield was formerly 
made quite small, and where the material penetrated is very 
soft, a short front-end construction yet has many advocates; 
but the general tendency now is to extend the cutting-edge far 
enough ahead of the diaphragm to form a fair-sized working 
chamber. Excavation is far more easy and rapid when the 
face can be attacked directly from in front of the diaphragm 
than where the work has to be done from behind through the 
apertures in the diaphragm. So long as the roof of the excava- 
tion is supported from falling, experience has shown that it is 
easily possible to extend the excavation safely some distance 
ahead of the diaphragm. In reasonably stable material, like 
compact -clay, the front face will usually stand alone for the 
short time necessary to excavate the section and advance the 
shield one stage. In softer material the face can usually be 
sustained for the same short period by means of compressed air; 
or the face of the excavation, instead of being made vertical, can 
be allowed to assume its natural slope. In the latter case a 
visor-shaped front -end construction, such as was used on some 
portions of the Clichy tunnel, is particularly advantageous. The 
following figures show the lengths of the front ends of a number 
of representative tunnel shields. 

City and South London . 1 ft. Mersey River .... 3 ft. 

St. Clair River 11.25" East River 3f " 

Hudson River 5| " BlackwaU 6.5" 

Two general types of construction are employed for the 
cutting-edge. The first type consists of a cast-iron or cast-steel 
ring, beveled to form a chisel-like cutting-edge and bolted to 
the ends of the forward shell plates. This construction was 
first employed in the shield for the London Tower tunnel, and 
has since been used on the City and South London, Waterloo 
and City, and the Clichy tunnels. The second construction 
consists in bracing the forward shell plates by means of right 



SUBMARINE TUNNELING 



255 



triangular brackets, whose perpendicular sides are riveted re- 
spectively to the shell plates and the diaphragm, and whose 
inclined sides slant backward and downward from the front 
edge, and carry a conical ring of plating. The shields for the 
St. Clair River, East River, and Blackwall tunnels show forms 
of this type of cutting-edge construction. A modification of 
the second type of construction, which consists in omitting the 
conical plating, was employed on some of the shields for the 
Clichy tunnel. This modification is generally considered to be 
allowable only in materials which have little stability, and which 
crumble down before the advance of the cutting-edge. Where 
the material is of a sticky or compact nature, into which the 
shield in advancing must actually cut, the beveled plating is 
necessary to insure a clean cutting action without wedging or 
jamming of the material. 

Cellular Division. — It is necessary in shields of large diam- 
eter to brace the shell horizontally and vertically against dis- 
tortion. This bracing also serves to form stagings for the 
workmen, and to divide the shield into cells. The following 
table shows the arrangement of the vertical and transverse 
bracing in several representative tunnel shields. 



Name of Tunnel. 


Diameter. 


Hori- 
zontal. 


Plates, 

DiST. 

Apart. 


Vert. 
Braces. 


Hudson River 

Clichy 


Ft. 

19 

19.4 
21 
24 

27 
11 


In. 
11 



6 

m 

8 

3 

4 


No. 
2 
2 
2 
2 
2 
None 


Ft. 

6.54 
6.54 
6.98 
7.12 
6.0 


No. 

2 
None 

3 
None 

3 

1 


St. Clair River 

Waterloo (Station) 

Blackwall 

East River 





Referring first to the horizontal divisions, it may be noted 
that they serve different purposes in different instances. In 
the Clichy tunnel shield the horizontal divisions formed simply 
working platforms; in the Waterloo tunnel shield they were 
designed to abut closely against the working face by means of 
special jacks, and so to divide it into three separate divisions; in 



256 TUNNELING 

the St. Clair tunnel they served as working platforms, and also 
had cutting-edges for penetrating the material ahead; and in 
the Blackwall tunnel shield they served as working platforms, 
and had cutting-edges as in the St. Clair tunnel shield, and in 
addition the middle division was so devised that the two lower 
chambers of the shield could be kept under a higher pressure of 
air than the two upper chambers. Passing now to the vertical 
divisions, they serve to brace the shell of the shield against ver- 
tical pressures, and also to divide the horizontal chambers into 
cells; but unlike the horizontal plates they are not provided 
with cutting-edges. The St. Clair, Hudson River, and Black- 
wall tunnel shields illustrate the use of the vertical bracing for 
the double purpose of vertical bracing and of dividing the hori- 
zontal chambers into cells. The Waterloo tunnel shield is an 
example, of vertical bracing employed solely as bracing. The 
vertical division of the East River tunnel shield was employed 
in order to allow the shield to be dissembled in quadrants. 

The Diaphragm. — The purpose of the shield diaphragm is to 
close the rear end of the shield and the tunnel behind from an 
inrush of water and earth from the face of the excavation. It 
also serves the secondary purpose of stiffening the shell diamet- 
rically. Structurally the diaphragm separates the front-end con- 
struction previously described from the rear-end construction, 
which will be described farther on; and it is usually composed 
of iron or steel plating reinforced by beams or girders, and 
pierced with one or several openings by which access is had 
to the working face. In stable material, where caving or an 
inrush of water and earth is not likely, the diaphragm is omitted. 
The shield of the Waterloo tunnel is an example of this con- 
.struction. In more treacherous materials, however, not only 
is a diaphragm necessary, but it is also necessary to diminish 
the size of the openings through it, and to provide means for 
closing them entirely. Sometimes only one or two openings are 
left near the bottom of the diaphragm, as in the St. Clair 
and Mersey tunnel shields; and sometimes a number of smaller 



SUBMARINE TUNNELING 257 

openings are provided, as in the East River and Hudson River 
tunnel shields. 

In highly treacherous materials subject to sudden and violent 
irruptions of earth from the excavation face, it sometimes is 
the case that openings, however small, closed in the ordinary 
manner, are impracticable, and special construction has to be 
adopted to deal with the difficulty. The shields for the Mersey 
and for the Blackwall tunnels are examples of such special 
devices. In the Mersey tunnel a second diaphragm was built 
behind the first, extending from the bottom of the shield upward 
to about half its total height. The aperture in the first dia- 
phragm being near the bottom, the space between the second and 
first diaphragms formed a trap to hold the inflowing material. 
The Blackwall tunnel shield, as previously indicated, had its 
front end divided into cells. Ordinarily the face of the excava- 
tion in front of each cell was left open, but where material was 
encountered which irrupted into these cells a special means of 
closing the face was necessary. This consisted of three poling- 
boards or shutters of iron held one above the other against 
the face of the excavation. These shutters were supported by 
means of strong threaded rods passing through nuts fastened 
to the vertical frames, which permitted each shutter to be ad- 
vanced against or withdrawn from the face of the excavation 
independently of the others. Various other constructions have 
been devised to retain the face of the excavation in highly 
treacherous soils, but few of them have been subjected to 
conclusive tests, and they do not therefore justify consid- 
eration. 

Rear-end Construction. — By the rear end of the shield is 
meant that portion at the rear of the diaphragm. It may be 
divided into two parts, called respectively the body and the 
tail of the shield. The chief purpose of the body of the shield 
is to furnish a place for the location of the jacks, pumps, motors, 
etc., employed in manipulating the shield. It also serves a 
purpose in distributing the weight of the shield over a large 



258 



TUNNELING 



area. To facilitate the passage of the shield around curves, 
or in changing from one grade to another, it is desirable to 
make the body of the shield as short as possible. In the Mersey, 
Clichy, and Waterloo tunnel shields, and, in fact, in most others 
which have been employed, the shell plates of the body have 
been reinforced by a heavy cast-iron ring, within and to which 
are attached the jacks and other apparatus. The latest opinion, 
however, seems to point to the use of brackets and beams for 
strengthening the shell for the purpose named, rather than to 
this heavy cast-iron construction. In the Hudson River, St. 
Clair River, and East River tunnel shields, with their long and 
strongly braced front-end construction to carry the jacks, the 
body of the shield, so to speak, is omitted and the rear-end con- 
struction consists simply of the tail plating. In the Blackwall 
shield, the body of the shield shell provides the space necessary 
for the double diaphragms and the cells which they inclose. In 
a general way, it may be said that the present tendency of 
engineers is to favor as short and as hght a body construction as 
can be secured. 

The tail of the shield serves to support the earth while the 
lining is being erected; and for this reason it overlaps the for- 
ward ring of the lining, as shown clearly by most of the shields 
illustrated. To fulfill this purpose, the tail-plates should be 
perfectly smooth inside and outside, so as to slide easily between 
the outside of the hning plates and the earth, and should also 
be as thin as practicable, in order not to leave a large void behind 
the lining to be filled in. In soils which are fairly stable, the tail 
construction is often visor-shaped; that is, the tail-plates overlap 
the lining only for, say, the roof from the springing lines up, as 
in one of the shields for the Clichy tunnel. In unstable materials 
the tail-plating extends entirely around the shield and excava- 
tion. The length of the tail-plating is usually sufficient to over- 
lap two rings of the lining, but in one of the Clichy tunnel shields 
it will be noticed that it extended over three rings of lining. 
This seemingly considerable space for thin steel plates is made 



SUBMAEINE TUNNELING 



259 



possible by the fact that the extreme rear end of the tail always 
rests upon the last completed ring of lining. 

In closing these remarks concerning the rear-end construction, 
the accompanying table, prepared by Mr. Raynald Legouez, 
will be of interest, as a general summary of principal dimensions 
of most of the important tunnel shields which have been built. 
The figures in this table have been converted from metric to 
English measure, and some slight variation from the exact di- 
mensions necessarily exists. The different columns of the table 
show the diameter, total length, and the length of each of the 
three principal parts into which tunnel shields are ordinarily 
divided in construction as previously described : 



Name of Shield. 



Concorde Siphon . . . 
Clichy Siphon .... 

Mersey 

East River 

City and South London 
Glasgow District . . . 
Waterloo and City . . 
Glasgow Harbor . . . 
Hudson River .... 
St. Clair River .... 
Clichy Tunnel .... 
Clichy Tunnel .... 

Blackwall 

Waterloo Station . . . 



Length in Feet. 


DLA.METER. 


Tail. 


Body. 


Front. 


Total. 


6.75 


2.51 


2.55 


1.16 


6.67 


8.39 


2.51 


2.55 


1.16 


6.16 


9.97 


5.61 


2.98 


2.98 


11.58 


10.99 


3.51 


0.32 


3.67 


7.51 


10.99 


2.65 


2.82 


1.01 


6.49 


12.07 


2.65 


2.82 


1.01 


6.49 


12.99 


2.75 


2.98 


1.24 


6.98 


17.25 


2.75 


2.98 


1.08 


8.49 


19.91 


4.82 


2.98 


5.67 


10.49 


21.52 


4.00 


2.98 


11.25 


15.25 


23.7-19.8 


4.00 


2.98 


6.88 


17.22 


23.8-19.4 


7.44 


11.90 


4.46 


23.65 


27.00 


6.98 


5.90 


6.59 


19.48 


24.86 


3.34 


5.51 


1.14 


10.00 



A shield of 60 or 100 tons weight can hardly be directed along 
the line of the proposed tunnel and also through curves and 
grades, especially when driven through loose or muddy soils. 
The tunnels of the New York and Hudson River Railroad under 
the Hudson, and the tunnel of the New York Rapid Transit 
Railway under the East River, show marked evidence of how 
troublesome this work is. To avoid these and other incon- 
veniences encountered in every shield, the Author has designed 
a new shield which was briefly described at page 251. 



260 



TUNNELING 



Jacks. — The motive power usually employed in driving 
modern tunnel shields is hydraulic jacks. In some of the earlier 
shields screw-jacks were used, but these soon gave way to the 
more powerful hydraulic device. The manner of attaching the 
hydraulic jacks to the shield is always to fasten the cylinder 
castings at regular intervals around the ins de of the shell, with 
the piston rods extending backward to a bearing against the 
forward edge of the lining. In the older forms of shield, having 
an interior cast-iron reinforcing ring construction, the jack 
cylinder castings were always attached to this cast-iron ring; 
but in many of the later shields constructed without this cast- 
iron reinforcing ring, the cylinder castings are attached to the 
shell by means of bracket and gusset connections. The number 
and size of the jacks employed, and the distance apart at which 
they are spaced, depend upon the size of the shield and the 
character of the material in which it is designed to work. In 
stiff and comparatively stable clays, the skin friction of the 
shield is comparatively small, and an aggregate jack-power of 

from 4 to 5 tons per square yard of 
the exterior friction surface of the 
shield has usually been found ample. 
The cylinders are spaced about 5| ft. 
apart, and have a working diameter 
of from 5 to 6 ins., with a water 
pressure of about 1000 lbs. per sq. in. 
In soft, sticky material, giving a 
high skin friction, the aggregate jack- 
power required per square yard of 
exterior shell surface rises to from 18 
to 24 tons; the jacks are spaced about 
3 ft. apart; and the working cylinder 
diameter and water pressure are, re- 
spectively, about 6 or 7 ins., and from 
4000 lbs. to 6000 lbs. per sq. in. With these high pressures, 
power pumps are necessary to give the required water pressure; 




Fig. 136. — Elevation and Section 
of Hydraulic Jack, East River 
Gas Tunnel. 



SUBMARINE TUNNELING 261 

but where the pressure required does not exceed 1000 lbs. per 
sq. in.; hand pumps may be, and usually are, employed. Fig. 
118 shows the hydrauHc jacks used in the East River Gas Tun- 
nel at New York. The number of jacks required depends upon 
the diameter of the shield, and, of course, upon the distance 
apart which they are placed. In the City and South London 
tunnel shield six jacks were used, and in the Blackwall shield 24 
were used. The mechanical construction of the jacks for tun- 
nel shields presents no features out of the usual lines of such 
devices used elsewhere. The jacks used on the East River tun- 
nel shield are shown by Fig. 136. 

Two general methods are employed for transmitting the 
thrust of the piston rods against the tunnel lining. The object 
sought in each is to distribute the thrust in such a manner that 
there is no danger of bending the thin front flange of the forward 
lining ring. In English practice the plan usually adopted is 
to attach a shoe or bearing casting to the end of the piston rod, 
which will distribute the pressure over a considerable area. An 
example of this construction is the shield for the City and South 
London tunnel. In the East River and St. Clair River tunnels 
built in America, the tail of the piston rod is so constructed that 
the thrust is carried directly to the shell of the lining. 

LINING. 

Either iron or masonry may be used for lining shield-driven 
tunnels but present practice is almost universally in favor of 
iron lining. As usually built, iron lining consists of a series of 
successive cast-iron rings, the abutting edges of which are pro- 
vided with flanges. These flanges are connected by means of 
butts, the joints being packed with thin strips of wood, oakum, 
cement, or some other material to make them water-tight. 
Each lining ring is made up of four or more segments, which 
are provided with flanges for bolted connections similar to 
those fastening the successive rings. Generally the crown seg- 
ment is made considerably shorter than those forming the sides 



262 



TUNNELING 



and bottom of the ring. The erection of the iron segments 
forming the successive rings of the Hning may be done by hand 
in tunnels of small diameter where the weights to be handled 
are comparatively light, but in tunnels of large size special 




Part Transverse Section. Longitudinal Section. 

Fig. 137. — Cast-iron Lining, St. Clair River Tunnel. 

cranes attached to the shield or carried by the finished lining 
are employed. The construction of the iron lining for the Hudson 
River tunnel is illustrated in Chapter XX., and that for the 
St. Clair River tunnel is shown by Fig. 137. 



SUBMARINE TUNNELING 263 



CHAPTER XX. 

SUBMARINE TUNNELING (Continued). 

THE SHIELD AND COMPRESSED AIR METHOD. THE HUDSON 
RIVER TUNNEL OF THE PENNSYLVANIA RAILROAD. 



The shield and compressed air method of excavating sub- 
aqueous tunnels is used when the distance is small between the 
roof of the tunnel and the bed of the river. These tunnels are 
usually driven from the shafts sunk from each shore. It is very 
seldom they can be driven also by an intermediate shaft. This, 
however, was done in the case of the Belmont tunnel under the 
East River. Here the tunnels passed under the man-of-war 
reef where a working shaft was sunk. 

The plant is located at some convenient point near the head 
shaft. It consists of a set of boilers to provide the power for 
the different machines. They are low and high pressure com- 
pressors, the former supply the air through the tunnel; the latter, 
the air for working the drills, in case rock is encountered, and 
power for hauling and hoisting purposes. The various pumps 
force the water for the hydraulic rams that drive the shield and 
work the erector. They also remove the water from the tunnel 
which always collects in variable quantities at the bottom of 
the excavation. Besides the machines for light and ventilation 
purposes, the head shaft is provided with an overhead con- 
stmction where are housed the hoisting machines, the telephone 
and other means of communication with the work at the front. 
Usually a long trestle is built in connection with the head shaft, 
leading to the dumping place and yard. On this inclined elevated 
structure are located, also, the tracks upon which will run the 
small cars used inside the tunnel for hauling purposes. 



264 TUNNELING 

The shafts are excavated on a square, rectangular or circular 
plan and are usually lined with masonry. It is only recently 
that shafts excavated through loose soils have been lined with 
the same cast-iron lining used in the tunnels, the only difference 
being that the rings were laid flat on the ground and attached 
to those already sunk. 

After the shaft has been sunk to the required level, the tunnel 
is driven toward the river by any one of the methods used for 
land work. At some convenient distance from the shaft, the 
dimensions of the tunnel are enlarged for a length of 20 or 30 ft. 
In this larger space, called the shield chamber, the shield is 
assembled, mounted, and, when completed, it is slowly pushed 
toward the river. The tunnel is excavated from the shield 
chamber on, with dimensions equal to the exterior shell of the 
shield. . 

The construction of the shield and the hydraulic jacks used 
for its advance are explained in a preceding chap+er. 

In very loose soils, a solid bulkhead of masonry is built across 
the tunnel, after the shield has advanced to a certain distance 
and some rings of the cast-iron lining have been erected. The 
bulkhead is provided with three air locks — two near the floor of 
the tunnel, for working purposes, and one near the roof, called 
the emergency lock, which, as the name suggests, is used only in 
case of danger. The air locks are steel cylinders from 10 to 
15 ft. long and 6 ft. in diameter, made up of boiler plates. They 
are provided with doors at each end, besides the pipes for the 
admission and exit of compressed air. The working locks also 
have narrow-gauge tracks for hauHng purposes. In rock or 
more consistent soil the bulkhead is constructed after the shield 
is far ahead, since there is no immediate necessity, under these 
conditions, to use the compressed air. In both the loose and 
good soils, when the shield has been advanced over 500 ft. from 
the bulkhead, a second bulkhead, with air locks, is erected in 
the tunnel. The first is left in place but used only in case of 
emergency. 



SUBMARINE TUNNELING 265 

To direct the shield along the center Hne and through curves 
and grades, accurate measurements are taken, and the distance 
between the shield and the last ring inserted in the iron lining 
is regulated accordingly. The alignment inside the tunnel is 
maintained in a very simple way. For this purpose, points 
corresponding to the center line are marked on the roof at 
distances of 100 ft. Nearly 100 ft. from the shield, a transit is 
set up on a strong scaffold spanning the tunnel, and it is sup- 
ported by the flanges of the iron lining. A plumb-line is hung 
from one of the points of the roof already determined, as indicat- 
ing the center line; and the transit man aligns his instrument 
with this plumb-line; after this he " plunges " his telescope. A 
rodman next places a horizontal rod of special construction 
between the flanges of the last ring of the lining. This rod has 
in the center an open slot which carries a glass with a black 
vertical line. The slot is graduated, the zero of graduation 
remains in the center while the vertical line is moved right and 
left. The rodman places a lamp behind the slot and the transit- 
man tells him how to move the dark line until it coincides with 
the axis of the tunnel. If the ring, just erected, be a little out 
of alignment, it is readjusted by pushing the shield a little more 
on the side that has swerved from the axis of the tunnel. As the 
shield is pushed forward, it is kept in place by four men with 
graduated rods, one man on each side of the shield, one on top 
and the other on the floor. As the shield progresses, they repeat 
aloud in succession, the distance indicated on the rods, which 
is the distance from the shield to the outer circumferential 
flange of the last ring of the lining. When an advance of one 
foot has been made, readings are taken at every inch ; and when 
very near the required distance, they are taken at every quarter 
of an inch. In this way it is not difficult to bring the shield back 
into line, in case it may have shifted a little to the right or left. 
AATien curves are met, the rings are no longer cylindrical segments 
but tores, so that the segments at one side are longer than 
those on the other. In this case, the shield is advanced more 



266 TUNNELING 

on one side by a quantity equal to the difference of the two sides 
of the ring to be erected. At each advance the shield is moved 
2 ft. or 2 J ft. ahead, the distance corresponding to the length of 
the cast-iron rings of the lining. Within the space now open 
between the shield and the lining another ring is inserted. The 
ring is composed of different segments provided with flanges 
and holes bored so they can be bolted together. The segments 
of the lining are very heavy and diflScult to handle but they are 
easily set by means of the erector. 

When the erector is not mounted on the shield, it is located 
in the middle of a girder placed across the iron rings of the lining 
and just at the rear end of the shield. The girder, at both 
extremities, has flanged wheels resting on rails which are placed 
on brackets. These brackets are attached temporarily to the 
flanges of. the iron lining. The erector is provided with an arm 
capable to swing in a full circle. Its movements are regulated 
by two hydraulic jacks, located horizontally on the spanning 
girder. On the extreme end of the revolving arm are projections 
with holes for the bolts. Each segmental plate of the lining 
has a kind of plug in the center which is cast together with the 
plate and is provided with holes for the bolt. In placing the 
segmental plates of the lining, the arm of the erector is swung 
over the plate to be lifted, then two bolts are passed through 
the holes in the projection of the erector, and through those in 
the plug. The arm of the erector is then moved upwards until the 
plate, free from all obstacles, is swung very near its intended 
position. There it is adjusted and held until bolts are inserted 
to fix it to the plates of the preceding ring. 

In connection with the method of excavating submarine 
tunnels by means of shield and compressed air, the excavation 
varies with the quality of soil encountered. In compact rock the 
usual heading and bench method, so common in land tunnels, is 
also employed in this case. The shield is left behind in presence 
of good rock. 

The men at the front attack the rock with air drilling machines 



SUBMARINE TUNNELING 267 

and charges of dynamite. The holes are driven at a smaller 
depth than in land work; very light charges of dynamite are 
used and only a few holes fired at each round. Every precaution 
is taken in order not to disturb the shield and the bed of the river 
any more than is possible, because at a shallow depth the blast 
would tend to widen the existing crevices in the rock and thus 
permit an inflow of water. When the rock is fissured or dis- 
integrated and the roof of the excavation at the front requires 
timbering, the shield should be kept closer to the front. In this 
way the quantity of timber for strutting is greatly reduced, so 
lessening the probabilities of fires. It is very difficult, in com- 
pressed air, to extinguish fires and in almost every instance the 
only way is to flood the tunnel. This was done at the Manhattan 
end of the tunnel under the East River for the extension to 
Brooklyn of the New York Subway. 

The excavation is made by hand in loose but compact soils 
such as clay. The men work on platforms located at the front 
of the shield and they are protected from the caving-in of the 
roof by a hood added for working through loose soils. The men 
excavate the material which is shoveled inside the tunnel and 
is carried away in small cars. The shield is very close to the 
front of the excavation in loose soil. The East Boston tunnel, 
under Boston Harbor, connecting with the Boston Subway, was 
excavated through blue clay. The minimum distance between 
the bottom of the water and the roof of the excavation was 18 ft. 
The tunnel was excavated by means of compressed air and the 
shield which was only used for the roof. It slid on top of concrete 
side walls built in two drifts which were excavated nearly 100 ft. 
ahead of the shield. The tunnel was lined with concrete, the 
arch being reinforced by longitudinal steel rods which received 
the thrust of jacks used for advancing the shield. The material 
in the drifts under the shield and the bench was removed by 
hand and carried away in small cars. 

Subaqueous tunnels driven through very loose soils can be 
excavated by simply leaving the doors open while the shield is 



268 TUNNELING 

pushed ahead. The material, dislodged by the cutting edge of 
the shield, is forced through the doors and falls on the floor 
whence it is removed in small cars. In very loose soils the 
excavation has been made in a still more economic way; the shield 
with closed doors is simply squeezed through the soil. This 
method is financially convenient, because all the excavating and 
hauling operations are eliminated and the tunnel progresses 
from 40 to 50 ft. per day, but clearly indicates a lack of stability. 
In this manner, the Hudson River tunnel of the New York and 
New Jersey Railroad was constructed. 

The pressure of the air in the tunnel depends upon the depth 
and as a rule it varies between 20 and 40 or even more pounds 
per square inch above atmospheric pressure. Working in com- 
pressed air causes a peculiar disease commonly known as ^^ bends " 
or '' caisson disease " often proving fatal. To prevent and 
remedy the disease, the engineers should order a set of rules to 
be strictly observed. The preventative measures should be, first, 
to employ only sober, strong and healthy men, never one who 
has not successfully passed the examination of the attending 
physician; second, to order the lock tenders never to allow any 
man in or out of the tunnel unless he has spent at least ten 
minutes within the locks. Both compression and decompression 
should be thorough and it cannot be in less than this time. A 
stop of only a few minutes in the locks is not sufficient and this 
incomplete compression or decompression is the real cause of the 
bends. The men become careless after they have been in the 
compressed air for some time, and they try to reduce this tire- 
some operation to a minimum, hence the duty of the engineer 
to strictly enforce this rule. The remedial measures should 
consist of constant medical attendance near the shafts and the 
erection of a compressed air hospital where the men affected 
by bends for lack of decompression may be attended and 
cured. 



SUBMARINE TUNNELING 269 

THE HUDSON RIVER TUNNELS OF THEj PENNSYLVANIA 
RAILROAD.* 

The tunnels constructed under the Hudson River for the Penn- 
sylvania Railroad, consist of two parallel tubes driven side by 
side 14 ft. apart. The tubes are of circular cross-section, 23 ft. 
exterior diameter, and are lined with cast-iron rings. The tunnels 
were driven from two shafts, one on the eastern shore of the 
Hudson River near 32nd St. and 11th Ave., New York; the other 
at Weehawken, New Jersey, near the piers of the Erie Railroad. 
The horizontal distance between the shafts was 6550 ft. The 
permanent one at Weehawken was built on a square plan, 130 ft. 
to a side. It was lined with concrete masonry and the walls 
were battered in such a way as to become the shape of an inverted 
frustum of a pyramid. It was provided with five openings at the 
bottom, four of these are used by trains that run in the open, 
the fifth one leads to a power house near by. During the con- 
struction of the tunnels one-third of this shaft was used for the 
land portion of the tunnel under Bergen Hill, while the remaining 
two-thirds were devoted to the construction of the tunnel under 
the river. The working shaft on Manhattan Island was a side 
shaft of rectangular plan 30 ft. by 22 ft., the tunnel proper being 
connected by two drifts 10 ft. by 10 ft. each. The shield rooms 
23 ft. long, were situated on both sides of the river just in front 
of the shafts. On the New York side, the shields, one for each 
tube, were built inside the iron lining of the shield chamber, 
and the hoisting tackle was slung from the iron lining. The 
erection on the Weehawken side was done in the bare rock 
excavation where timber falsework was used. After the shields 
were finished and in position, the first two rings of the lining 
were erected in the tail of the shield. These rings were firmly 
braced to the rock and the chamber lining; then the shields 
were shoved ahead by their own jacks, another ring was built 
and so on. 

* Condensed from paper by James Forgie, " Eng. News," Vol. LVI, and by H. B. Hewett 
and W. L. Brown, " Proc. Am. Soc. C. E.", Vol. XXXVI. 



270 



TUNNELING 



Shield. — The shields used in these tunnels were designed by 
Mr. James Forgie, M. Inst. C. E. and M. Am. Soc. C. E., and 
were provided with three innovations : the segmental doors, the 
sliding platforms and the removable hood. The shields, Fig. 138, 




Half -jecrion A- 



Horizontol S€ci-lon. 
Fig. 138. — General Elevations and Sections of Shield. 



were circular, 23 ft. 6i ins. in external diameter, and were 16 ft. 
long, exclusive of the hood. The tail of the shield overlapped 
the lining, the maximum being 6 ft. 4 J ins. during ordinaiy 
working; the minimum, 2 ft. during the operation of taking any 



SUBMARINE TUNNELING 271 

ram out for repairing. The shields had only one transverse 
bulkhead made up of two continuous horizontal platforms and 
three vertical partitions stiffening angular web plates fore and 
aft the ram chambers. They were connected by angles and skin 
plates which formed a ring-shaped frame 25 ins. thick radially 
and nearly 5 ft. long. Between the vertical and horizontal 
partitions were left openings which either were partially or 
entirely closed by segmental doors pivoted on an axis parallel 
to the face of the shield bulkhead. There were nine of such 
openings on each shield, the clear width being 2 ft. 7 ins., the 
height varying from 2 ft. 2 ins. to 3 ft. 4 ins., according to the 
location. The hood at the front of the shield was designed so 
as to be detached underground and was made of complete 
segments to permit easy erection or detachment. The hood 
was extended as far as the upper platform, thus protecting only 
the roof of the excavation. It was attached to the shield by 
means of bolts, and, when removed, it was replaced by the cast- 
steel cutting-edge, built in 24 sections and placed all around the 
shield. The eight sliding platforms, another characteristic of 
this shield, could be extended 2 ft. 9 ins. in front of the shield 
by means of hydraulic rams, and, when so extended, were able 
to stand a pressure of 7900 lbs. per sq. ft. These sliding plat- 
forms w^ere used as hoods for the protection of the men working 
through loose soils, while in rock they enabled the drilling and 
blasting to be carried on at three levels. A water trap or bird 
fountain was constructed, at the rear of the bulkhead of the 
shield, by means of angle irons to which steel plates were bolted. 
The opening to the face was so spacious that in an emergency 
the men could readily escape by getting over this trap into 
safety. Besides, with the assistance of compressed air, it was 
sufficient to perfectly trap the water-bearing ground, in case the 
face collapsed. Including rams and erector, the total weight of 
the shield was 193 tons. 

Hydraulic Rams. — The shield w^as operated by hydraulic 
pressure. The machines were designed for a maximum pressure 



272 TUNNELING 

of 5000 lbs., to a minimum of 2000 lbs., while the average work- 
ing pressure was 3500 lbs. per sq. in. The forward movement 
of the shield was obtained by means of 24 single-acting rams 
8J in. in diameter and with 38 in. stroke. Each ram exerted a 
pressure of nearly 100 tons, so that the combined action of the 
24 rams was equal to 2400 tons. Each sliding platform was 
operated by two single-acting rams 3 J ins. in diameter and with 
2 ft. 9 in. stroke. The rams were attached to the rear face of 
the shield and the front ends of the cylinders to the front ends 
of the sliding platforms, and since the cylinders were movable 
and free-sliding so also were the platforms. 

Erector. — The erector, a box-shaped frame mounted on a 
central shaft, revolved in bearings attached to the shield. Inside 
this frame there was a differential hydraulic plunger of 4 in. 
and 3 in. diameters and 48 in. stroke. To the plunger head 
were attached two channels which slide inside the box frame and 
to the projecting ends of which the grip was attached. At the 
opposite end of the box frame was attached a counter-weight 
which balances about 700 lbs. of the tunnel segment at 11 ft. 
radius. The erector was revolved by two single-acting rams 
fixed horizontally to the back of the shield, above the erector 
pivot, through double chains and chain wheels which were 
keyed to the erector shaft. 

Air Locks. — Two bulkhead walls, forming the rear closure 
of the pneumatic sections, were built in each end of each tunnel, 
one just ahead of the shield chamber, the other about 1200 ft. 
ahead of the first. The walls were built of Portland concrete 
10 ft. thick, and they were grouted with Portland cement, under 
a pressure of nearly 100 lbs. per sq. in., to make them thoroughly 
air-tight. Each wall had in it three locks; for man, material and 
emergency. Each was equipped with hand valves arranged to 
be operated from either outer end or from within. The floors 
of the man and material locks were on a level with the working 
platform of the tunnel, about 3 ft. 6 ins. above the invert; the 
floor of the emergency lock was about 5 ft. above the horizontal 



SUBMARINE TUNNELING 



273 




Sec+jonal 



£ 



E30 



^^Hiqh Pressuf>e^Air^ 



[. .i ; .-^ ." ■ ■ i; ji :T| 'j . V *.■ 



flrv jlll 



axis of the tunnel. The 
locks were made of steel 
plates and shapes, with iron 
fittings riveted and bolted 
together. The man lock 
was 11 ft. long of ellip- 
tical cross-section, 6 ft. 
vertical diameter and 5 ft. 
horizontal ; the material 
lock was 25 ft. long, with 
circular cross-section, 7 ft. 
diameter, and the emer- 
gency lock was 20 ft. long, 
of elliptical cross-section, 
4 ft. vertical and 3 ft. hori- 
zontal diameters. Fig. 139 
shows the elevation of the 
air lock used in the Penn- 
sylvania tunnel. 

Excavation. — In driv- 
ing these tunnels almost 
any kind of material was 
encountered, viz., rock, 
partly rock, and partly 
loose soil, sand and gravel, 
and finally silt. 

Rock. — Much of the 
rock excavation was made 
before the shields were 
erected in orderto avoid the 
handling of rock through 
the narrow openings of the 

shield doors. Throughout the cross-section the shield traveled 
on a cradle of concrete in which 2 or 3 steel rails were imbedded. 
At the points where the excavation had been made for the full 



tell I :i?fl::■^^^^^l;v■^;!-:|:v|^^ 

,i[ 1 ;t i; Man Lock y\ \-%.\-[' \ :.-:[' ' H 'vi- rll If:':: 




Fig. 



Horizontal ' Section 
139. — Plan and Elevation of First Bulkhead 
Wall in South Tube Manhattan. 



274 TUNNELING 

section of the tunnel, it was only necessary to trim off the 
projecting corners of rock. Where only the bottom heading 
had been driven the excavation was completed just in front of 
the shield; the drilling below the axis level being done from 
the heading itself, and above that from the front sliding plat- 
forms of the shield. The holes were placed near together and 
were drilled short; very light charges of powder were used in 
order to lessen the chance of knocking the shield about too 
much. 

Mixed Face. — When the rock dipped to such an extent that 
the front of the tunnel was excavated partly in rock and partly 
in loose soil, the compressed air was turned on, starting with a 
pressure varying from 12 to 18 lbs. When the surface of the 
rock was penetrated, the soft face was held up at first by hori- 
zontal boards braced from the shield until the shield was shoved. 
The braces were then taken out and, after the shield had been 
shoved, were replaced by others. As the amount of soft ground 
in the surface increased, the system of timbering was gradually 
changed to one of 2-in. poling-boards. These rested on top of 
the shield and were supported by vertical breast-boards which 
in turn were held by 6-in. by 6-in. walings, braced through the 
upper doors to the iron lining and from the sliding platforms of 
the shield. 

Sand and Gravel. — Sand and gravel were only met at Wee- 
hawken, where two different methods were used. The first 
method was employed when the roof of the excavation was 
through sand. It consisted of excavating the ground 2 ft. 6 ins. 
ahead of the cutting-edge, the roof being held in place by longi- 
tudinal poling-boards. These boards rested on the outside of 
the skin at their back end, and at the forward end on vertical 
breast-boards, braced from the sliding platforms and through 
the shield doors to cross timbers in the tunnel. 

The second method of timbering was used in the presence of 
gravel at the upper part of the excavation. In such a case, the 
excavation was only carried 1 ft. 3 ins. (half a shove) ahead of 



SUBMARINE TUNNELING 275 

the cutting-edge, the roof being supported by transverse boards 
held by pipes which rested in holes left in the shield. After a 
small section of the ground had been excavated a board supported 
by a pipe that was inserted underneath and wedged to it was 
placed against the ground. These polings were kept below 
the level of the hood, so that when the shield was shoved, they 
would come inside of it ; in addition they were braced with vertical 
posts from the sliding platform. The upper part of the face was 
held by longitudinal breast-boards braced from the sliding plat- 
form by vertical pieces. The lower part of the face was supported 
by vertical sheeted poling, braced to the tunnel through the 
lower doors. Straw and clay were used in front of the boards to 
prevent the escape of air which was very large, when the tunnel 
was excavated through sand and gravel. The average rate of 
progress in these materials was 5.1 ft. per day. 

Silt. — When silt was encountered, the shield was shoved into 
the ground without any excavation being done by hand ahead 
of the diaphragm. As the shield advanced the silt was forced 
through the doors into the tunnel. Forcing the shield through 
the silt resulted in raising the bed of the river, the amount that 
the bed was raised depending on the quantity of material 
brought into the shield. When the whole volume of the excava- 
tion was brought in, the surface of the bed was not affected; 
when about 50% was taken in, the surface was raised about 3 ft.; 
if the shield was driven blind, the bed was raised about 7 ft. 
When the shield was driven bhnd, the tunnel began to rise for 
about 2 ins., and the iron lining was distorted, the vertical 
diameter increasing and the horizontal one decreasing by about 
IJ ins. It was found, however, that the tunnel was not affected 
when part of the excavation was taken, but if all of it was taken 
in or the shield was shoved with open doors, the tunnel was 
lowered. A powerful aid was thus found for the guidance of 
the shield; for, if high, the shield could be brought down by 
increasing the quantity of muck taken in, if low, by decreasing it. 

The junction of the shields under the river was made as 



276 TUNNELING 

follows: When the two shields of one tunnel, which had been 
driven from opposite sides of the river, approached within 10 ft. 
of each other, they were stopped; a 10-in. pipe was driven be- 
tween them, and a final check of lines and levels was made 
through the pipe. One shield was then started up with all doors 
closed, while the doors of the stationary shield were opened for 
the muck driven ahead by the moving shield. This was con- 
tinued until the cutting-edges came together. All doors in both 
shields were then opened and the shield mucked out. The 
cutting-edges were taken off and the shields moved together 
again, edge of skin to edge of skin. As the sections of the 
cutting-edges were taken off, the space between the skin edges 
was poled with 3-in. stuff. ^Vhen everything except the skin had 
been removed, iron lining was built up inside the skins ; the gap 
at the junction was filled with concrete and long bolts were used 
from ring to ring on the circumferential joint. 

Lining. — The tunnels were lined with cast-iron circular rings 
of the segmental bolted type. In some special cases, cast steel 
was used instead of cast iron. The rings were made 30 ins. long, 
with an internal diameter of 21 ft. 2 ins. and an external one of 
23 ft. The rings were composed of nine equal segments of 77 J 
ins. external circumferential length each, except the two segments 
adjoining the key which were equal to the other segments with 
the difference, that one end joint was not radial but formed so as 
to make an opening 12.25 ins. wide at the outside and 12.60 ins. 
at the inside, which was closed by the key segment. Each seg- 
ment had six bolts in the circumferential joint, the key had one, 
so that there were 67 bolts in one circumferential joint. Each of 
the twelve longitudinal or radial joints had five bolts, in all 
127 bolts per ring. The circumferential flanges of each plate 
were strengthened by two transverse webs or feathers on each 
flange. Each segment was provided with a IJ-in. grout hole 
closed with a screw plug. In order to pass around curves, 
whether horizontal or vertical, or to correct deviation from the 
line or grade, tapering was used ; by this is meant the placing of 



SUBMAEINE TUNNELING 277 

rings in the tunnels which were wider than the standard rings, 
either at one side (horizontal tapers or liners), or at the top 
(depressors), or at the bottom (elevators). Tapers J, f or even 
1 in. were used. The taper rings were made by casting a ring 
with one circumferential flange much thicker than usual and 
then machining it off to the taper. 

Grouting^. — From the exterior of the tunnel already lined 
with cast-iron rings, grout was forced through the holes closed 
by screw-plugs, at a pressure of 90 lbs. per sq. in. The grout was 
composed of 1 Portland cement and 1 sand by volume and was 
forced in by a specially constructed machine, so it formed a shell 
of cement nearly 3 ins. thick around the exterior of the iron 
lining. The grouting began at the lower segment; the cement 
was forced in until it reached the hole above, then the hole was 
plugged, and the grouting was carried on from the consecutive 
hole and so on until all the tunnel was finally encased in grout, 
as it filled every crevice between the outside of the lining and 
the ground as excavated. The cast-iron rings of the tunnel were 
covered with a concrete lining which was placed in the following 
order: First, on the invert; second, on the duct benches; third, 
on the arch; fourth, on the ducts; fifth, on the face of the bench. 
Before any concrete was placed, the surface of the iron was 
cleaned by scrapers and wire brushes and by washing it with 
water. The invert was built in sections 30 ft. long and the duct 
benches were constructed soon after. These duct benches were 
built with several steps for the ducts to be laid later. They were 
built by means of a traveling stage on wheels which ran on 
tracks on the working platform of the tunnel. The arch was 
constructed soon after. First the portion from the duct benches 
to the haunches, then the arch proper, was built on traveling 
centers on tracks laid on the steps of the duct benches. The 
concrete was received in |-cu.-yd. dumping buckets, from the flat 
cars on which they were run; the buckets were hoisted to the 
level of the lower platform of the arch by a small Lidgerwood 
compressed air hoister. At this level the concrete was dumped 



278 



TUNNELING 



on a traveling car or stage and moved in that to the point on the 
form where it was to be placed. For the lower part of the arch 
the concrete was thrown directly into the form from this travel- 
ing part of the stage. Fig. 140 shows the cross-section of the 
tunnel with the iron lining and concrete. 

Hauling. — A working platform, made up of 5-ft. sections, 
was built inside the tunnel and kept close to the shield. On 
this platform two lines of industrial railway tracks with switches 
and sidings at the locks, and a heading, were laid for hauling 
materials and spoils. These lines converged into a single track 



Sc^fTTfffTtS^ 



W^||_5^5ft^5g-V._ 





Section to Sand and Gravel or Kock 

Section In Hudson Jliver Silt, with foundatlona 
Fig. 140. — Typical Cross-Sections of One Tube of Pennsylvania Railroad Tunnel Under 

the Hudson River. 

in passing through the air locks. At the shaft elevators, they 
terminated in a steel plate floor to avoid switches. Between the 
locks of the bulkheads was installed an electrically driven cable 
system, to haul the loaded muck up grade and to empty the flat 
cars. From the first bulkhead to the shaft, the cars were hauled 
up grade by a steam hauling engine. At the Manliattan end 
there was one 10-H.P. engine for each tunnel, while at Wee- 
hawken one 25-H.P. engine served for both tunnels. Each shaft 
contained two elevators driven by a double-cable, reversible 
single-drum steam-hoisting engine. A grouty frame was built 



SUBMARINE TUNNELING 279 

over the shafts, and on the platforms over this frame were narrow- 
gauge tracks, extending from the elevators to the muck-chutes 
and to points where the lining segments were loaded on the cars. 
The elevators were arranged to stop at both the ground and the 
grouty platform levels. The rolHng-stock at each of the tunnels 
consisted of 75 flat cars for moving the tunnel segments, and of 
about 50 muck cars, each of IJ cu. yd. capacity. 

Plant. — The plants located at each end of the tunnel near the 
shafts were almost identical. Each consisted of three 500-H.P. 
Stirtling boilers, which supplied steam at 150 lbs. pressure. 
Feed water was supplied by three 13^ metropolitan injectors, and 
two Blake duplex pumps. Two Worthington surface condensers, 
each of 2250 sq. ft. condensing surface, took care of the exhaust 
from the engines and compressors. Condensing water was 
pumped from the river through a 16-in. pipe. The high-pressure 
air was supplied by a duplex Ingersoll-Sergeant compressor, 
with cross-compound steam end 14 X 26 X 30 ins. and simple 
water-jacket air cylinders 13J X 36 ins. Its capacity at 100 r.p.m. 
was 1085 cu. ft. free air per minute. The maximum pressure 
was 130 lbs. per sq. in. The air for the pneumatic working 
was supplied by three 14x26x30 in. duplex Ingersoll-Sergeant 
compressors. The maximum capacity of the three was 12,000 
cu. ft. free air per minute at 125 r.p.m. and a discharge pressure 
of 50 lbs. per sq. in. The suction air was taken from the outside 
about 10 ft. above the roof of the engine house. Three after- 
coolers, 32J ins. X 11 ft. 4 ins., each having 809 sq. ft. cooling 
surface of tinned brass tubes, cooled the low-pressure discharge 
to within 10° F. of the temperature of the cooling- water. From 
the aftercoolers, the air passed into three steel receivers each 
54 X 12 ft., placed outside the engine room and fitted with weigh- 
ing safety valves. The receivers were connected to two 10-in. 
mains; one serving the north, the other the south tunnel. A 
fourth receiver of the same size was built to receive the discharge 
of the high-pressure compressor, through a 4-in. pipe. The 
high-pressure water required for the shield was furnished by 



280 TUNNELING 

three Blake direct-acting, duplex pumps with outside packed 
plungers- The steam end was 16 X 18 ins., the water end 2tV X 18 
ins. At 55 r.p.m. pumping against 5000 lbs. per sq. in., the 
capacity of each pump was 57 gals, per minute. Two of them, 
one on each tunnel, were sufficient to run the shields and the third 
was held in reserve. The high-pressure water was conveyed to 
the front by means of a 2-in. double, extra strong pipe which was 
buried between the engine room and the shaft, in a trench, to 
prevent freezing in cold weather. The electric current for light 
and power was supplied by two 100-K.W. 250-volt G.E. direct- 
current generators directly connected to Ball & Wood high-speed 
engines running at 250 r.p.m. The switchboard had two machine 
panels, two distributing panels and one panel carrying a circuit 
breaker for the traction circuit. 

niumination. — The tunnel was lighted by electricity, there 
being two rows of lamps, one in the crown and one in the south 
axial line. The lamps were 16-c.p., 240-volt, two-wire system, 
and were spaced 35 ft. apart in the crown and 12 J ft. apart on 
the axial line. In addition, five nests of 5 lamps each were 
used at the front. Candles were supplied for miscellaneous and 
emergency uses. The sockets for electric globes were fitted to a 
wooden reflector^ coated with white enamel paint on the inside. 



SUBMAKINE TUJSNELING 281 



CHAPTER XXI. 

SUBMARINE TUNNELING (Continued); TUNNELS 
AT VERY SHALLOW DEPTH. THE COFFER- 
DAM METHOD. THE PNEUMATIC CAISSON 
METHOD. THE JOINING TOGETHER SEC- 
TIONS OF TUNNELS BUILT ON LAND. 



The tunnels on the river bed or at such a shallow depth that 
only a few feet of material will remain between the bottom of the 
river and the roof of the tunnel can be built in three different 
ways, viz., (1) by a cofferdam; (2) by pneumatic caissons; (3) 
by sinking and joining together whole sections of tunnels that 
were built on land. 

The Cofferdam Method. — The Van Buren Street Tunnel, Chicago 
River. — According to the cofferdam method, the work is at- 
tacked at one of the shores, and the tunnel built in sections of 
such length as not to interfere with the flow of water or the 
navigation of the river. Round the entire exterior line of the 
first section a double-walled cofferdam is built, and strongly 
braced transversely, so as to withstand the pressure of the water. 
When the water is pumped out, a single-walled cofferdam is 
built within the first, leaving sufficient distance between the two 
to allow of the construction of the masonry. The soil is then 
removed within the inner cofferdam, and the tunnel constructed 
from the foundation. When the end of the tunnel reaches the 
channel end of the cofferdam, a crib-wall is erected over the end 
of the completed tunnel. This crib, in turn, forms the end wall 
of another cofferdam, built in continuation of the first, so as to 
allow the second section to be proceeded with, and at the same 
time to facilitate the removal of the cofferdams of the first 



282 TUNNELING 

section. The work goes on continuously in this way until the 
distant shore is reached. 

VAN BUREN STREET TUNNEL, CHICAGO. 

The Van Buren Street tunnel, built to carry a double-track 
street railway under the Chicago River, was completed in 1894 
by the cofferdam method. The special features of the tunnel* 
are: (1) the unusually large dimensions of the cross-section of 
30 ft. X 15 ft. 9 ins.; (2) its construction inside of cofferdams 
of great length and width; (3) the construction under some 
very high buildings calling for great care and very strong tem- 
porary and permanent supports. 

The special feature of the work for our present purpose was 
the construction of the tunnel across the river. To accomplish 
this a cofferdam was built out from the west shore of the river 
to its middle, and the tunnel constructed within it like the 
building of any other structure within a cofferdam. Trans- 
verse and longitudinal sections of this cofferdam are shown by 
Fig. 119. As will be seen, it was a simple double-wall coffer- 
dam, with a clear width between the walls of 58 ft., and braced 
transversely as shown. Inside of this a single-wall cofferdam 
of piles was constructed, with a clear width just sufficient to 
allow the construction of the masonry within it. When the 
tunnel end reached the channel end of the cofferdam, a crib-wall 
was built over the end of the completed tunnel, as shown by 
the drawings. This crib-wall was intended to form the end wall 
of another cofferdam, which was built out from the east shore, 
and within which the remaining half of the tunnel was built 
as the first half had been. The drawings show the character 
of the tunnel masonry and of the centering upon which it was 
built. 

The Van Buren Street tunnel was the last of the three tunnels 
under the Chicago River, constructed according to the cofferdam 
method. At the time the tunnels were constructed the bed of 

*" Eng. News," April 12, 1892. 



SUBMARINE TUNNELING 



283 




284 TUNNELING 

the river was 17 ft. deep. In connection with the harbor and 
river improvements, the Federal Government ordered the Chicago 
River to be lowered so as to give a depth of 26 ft. of water. This 
necessitated the lowering of the tunnel roof and the excavation 
for a deeper floor which was a very difficult operation. This 
work was described in ^'Eng. News/' Sept., 1906. 

THE PNEUMATIC CAISSON METHOD. — THE TUNNEL UNDER 
THE HARLEM RIVER. 

In the early seventies Prof. Winkler proposed to construct 
a tunnel under the River Danube to connect the various por- 
tions of the Vienna, Austria, underground railway, and to use 
caissons in the construction. Prof. Winkler proposed to build 
caissons from 30 ft. to 45 ft. long, with a width depending upon 
the lateral dimensions adopted for the tunnel masonry. The 
caisson was to be made of metal plates and angle iron with 
riveted connections on all sides except those running vertically 
transverse to the tunnel axis, whose connections were to be 
bolted. In the middle of the roof an opening was to be left; 
this was for the shaft having the air-locks to allow the passage 
of men, materials, and compressed air. 

Across the river two parallel rows of piles were to be driven 
into the river bed, to fix the place where the caisson was to be 
sunk. Then the first caisson near the shore was to be lowered 
in the ordinary way, and a second caisson was to be immediately 
sunk very close to the first one. When both caissons had 
reached the plane of the tunnel floor, the sides which were in 
contact were to be unbolted and removed, and the small space 
between made water-tight. The chambers of the two caissons 
were to be opened into a single large one communicating above 
by means of two shafts. At the same time that the masonry 
was being built in the first two caissons, from the inverted arch 
up, a third caisson was to be sunk; and when by excavation it 
had reached the plane of the projected tunnel floor, the partitions 
were to be removed so that the three caissons were in communi- 



SUBMARINE TUNNELING 285 

cation, forming a large single caisson. Then the outer partition 
of the first caisson was to be removed, and the masonry of the 
submarine tunnel connected with the portion of the tunnel built 
on land. In a similar manner all the caissons were to be sunk; 
and when the last one was placed, and the masonry lining con- 
structed, and connected with the portion of the tunnel built 
on the other shore of the river, the partition walls were to be 
battered down, and the submarine tunnel completely constructed 
and open to traffic. 

The Harlem River Tunnel. — The pneumatic caissons method 
was employed in the construction of the tunnel under the Harlem 
River for the New York Rapid Transit Railway. The tunnel 
proper consisted of two parallel tubes riveted to each other 
and surrounded by a cradle of concrete as shown in Fig. 121, 
page 216. The tunnel was built in three sections : — The first, 
from the Manhattan shore well towards the middle of the river; 
the second, from the shore of the Bronx towards the middle of 
the river; and the last, the section uniting the other two and 
completing the tunnel. 

Each section was built within a specially constructed working- 
chamber, consisting of timber side walls forming a wooden 
caisson, so constructed that compressed air could be used. This 
working-chamber of Mr. McBean presented some novel features, 
inasmuch as the caisson was not built on land, but under water. 

In building the tunnel, the Harlem River was dredged to a 
certain depth, so as to leave only 6 ft. or 8 ft. of excavation to 
be done before reaching the line of sub-grade of the proposed 
structure. Two service platforms were built on piles 10 ft. 
apart longitudinally, and cut off at a point above mean high- 
water mark, braced in the usual manner, and covered with heavy 
planks, to serve as the floor of the platform. On this platform 
were placed rails for the trains used in the transportation of 
materials. These platforms were also used in maintaining the 
perfect alignment of the caissons. 

Within the platforms and along the dredged channel four 



286 



TUNNELING 




Fig. 142. — Showing Working Platforms 
and Piles Sunk in the Dredged Channel. 



longitudinal rows of piles were sunk. These piles were accurately 
brought to line by beams bolted together, and placed across and 
above the water-level. A few beams were also added for the 
purpose of bracing the piles transversely, after which they were 
cut off under water and capped. 

Fig. 142 shows the manner in which the working platforms 
were constructed, and also the rows of piles sunk in the dredged 

channel. Between the piles a very 
'^ strong frame was placed, made up 
of waling pieces and two trans- 
verse beams 14 ins. by 14 ins. each, 
placed one below the other at a 
distance of 5 ft. 8 ins., and strongly 
braced together. Guiding-beams 
were fixed on each side of the 
frame for the sheeting piles. The 
frames were built in sections 
of different lengths, and placed 
directly above the cap-pieces of the pile-bents sunk in the 
dredged channel. 

The longitudinal sides of the caisson were constructed by 
sinking two rows of sheeting piles, each row being close to a 
service platform. The sheeting piles were made up of yellow- 
pine timbers 12 ins. by 12 ins.; three piles bolted together formed 
a section 3 ft. wide. Each section was grooved and tongued, so 
as to be firmly connected with the adjacent sections to be sunk. 
The lower ends of the piles were cut wedge-shaped, with a sharp 
edge to offer a small resistance while penetrating the soil. The 
sheeting-piles were then cut off under water, which operation was 
successfully carried out by means of a circular saw operated 
by a pile-driving machine. The sheeting was also extended 
between two platforms to make a bulkhead, and in this way the 
four sides of the caisson were built up. Particular attention 
was always given to the alignment of the sheeting piles, which 
was obtained by guiding the piles with the timbers placed longi- 



SUBMARINE TUNNELING 



287 



\, 



mi 



:y 



/ 



Fig. 143. — Showing Sheeting-Piles for the 
Sides of the Caisson and Trussed Beam for 
theRoof. 



tudinally, one below the water-line in connection with the frames 
located between the pile-bents, and the second along the inner 
edge of the service platform, as 
shown in Fig. 143. 

The caisson was completed 
by placing a roof covering the 
sides. This roof was 40 ins. 
thick, made up of three layers 
of 12-in. beams placed trans- 
versely to the axis of the cais- 
son, while between the beams 
planks 2 ins. thick were placed 
lengthwise and bolted together, 

so as to make a firm, solid structure. The roof was built ashore, 
in sections each varying from 39 ft. to 130 ft. long. The edges of 
the roof fitted the sides of the caisson perfectly; and when each 
section was towed to the proper spot, it was sunk and made 
secure. Under the roof were placed six longitudinal beams, 

12 ins. by 14 ins., called 
'' rangers," resting on the cap- 
pieces of the pile-bents that 
were laid across the space of 
the proposed tunnel; while the 
extreme rangers were used for 
the purpose of fitting above 
the sheeting-piles of the cais- 
son, in order to make the lat- 
ter water-tight. The two ex- 
treme rangers were provided 
with T-irons, the flat side being laid on the sheeting-piles, while 
the web penetrated the ranger by reason of the weight of the load 
resting on the roof, for the purpose of sinking it to the required 
point. Earth was next heaped on the roof, and in this way a 
large working-chamber was prepared, as shown in Fig. 144. 
The working-chamber built on the Manhattan side of the 




Fig. 144. — Showing the Caisson with the Work- 
ing-Chamber. 



288 TUNNELING 

Harlem River was 216 ft. long, provided with two rectangular 
shafts 7 ft. by 17 ft., rendered water-tight, and rising above the 
high-water mark of the river. Within these shafts the air-locks 
of the tunnel tubes were placed, so that the work could be carried 
on by means of compressed air. The pressure of the air was used 
to expel the water, being sufficiently intense to equilibrate a 
column of water equal to the depth of the lowest point of the 
roof of the caisson. 

"When the working-chamber was constructed, the tunnel 
proper was begun by excavating the soil down to the required 
level; the concrete was then laid on. It was just at this point, 
when a large part of the roof was constructed and supported only 
by the sheeting-piles of the sides of the caisson, that the writer 
of this article feared that this novel method of tunneling would 
prove a failure. The tendency of the timber to float, aided as 
it was by the air pressure within the caisson, was counteracted 
only by the weight of the earth heaped on the roof, and by the 
friction of the soil against the feet of the sheeting-piles. This 
friction was only a small quantity, as the soil was loose, so that 
it was considered rather risky and dangerous to place reliance on 
such a feeble quantity. This fear was, unfortunately, justified 
on two occasions, when on cutting off a portion of the pile-bents 
some of the sheeting-piles got loose and water flooded the whole 
chamber, but, happily, without loss of life. As the chamber was 
one of large dimensions, the workmen had time enough to effect 
their escape. It may be remarked that during these troubles 
only a few of the sheeting-piles were displaced, while the caisson 
itself offered a stout and successful resistance, due to its being 
strongly braced transversely. The accidents were, therefore, 
limited to a few piles, instead of affecting the entire caisson. On 
the occasion of the first, the repairs were effected by sinking the 
piles to a greater depth, continuing down until rock was encoun- 
tered. After that, the water was pumped out and the work 
resumed. In repairing the second accident, the sheeting-piles 
were driven down to bed-rock, and the surrounding soil strength- 



SUBMARINE TUNNELING 



289 




Fig. 145. 



■Showing the Tunnel Constructed 
within the Caisson. 



ened by cement forced through the loose soil around the piles. 
This remedy proved effective, and no further trouble occurred 
to delay the work on the Manhattan side of the Harlem River. 

On the concrete bed of the tunnel the segments of the metal 
lining were placed and sur- 
rounded by concrete, as re- 
quired by the plans and speci- 
fications (Fig. 145). The con- 
tractors had planned to unbolt 
the roof from its holdings, to 
remove by means of dredgers 
the earth which had been 
heaped on it, and thus set the 
roof afloat, after which it was 
to be towed within the two 

working platforms already erected on the Bronx shore. But 
Mr. McBean devised a simpler and more economic, but at the 
same time more dangerous, way of constructing this second 
section of the tunnel. He thought that the upper half of the 
tunnel proper could be used instead of the timber roof, thereby 
reducing the capacity of the working chariiber, and limiting the 
use of compressed air. In this way he dispensed with the 
removal of timber, and also of the earth heaped on the roof. 

In building this Bronx section, a channel was dredged along 
the line of the tunnel to a depth of 5 ft. from the foundation-bed 
of the proposed tunnel . The working platforms were constructed 
on both sides of this channel, quite similar to those erected on 
the other half of the tunnel; and between them pile-bents were 
sunk, capped with 12-in. by 12-in. beams. Over the cap-pieces 
rangers were placed longitudinally, which also rested on the sides 
of the wooden working caisson. Fig. 146. The sheeting-piles 
were cut off at level, but much lower down than in the first half 
of the tunnel. 

The roof was built on floats made of 12-in. by 12-in. timber laid 
transversely 4 ft. apart and supporting a floor of 3-in. by 12-in. 



290 



TUNNELING 




Fig. 



146. — Showing Sides of the Caisson and 

Supports for the Roof. 



planks rendered water-tight. The sides of the floats were made 
by verticals, 4 ins. by 6 ins., and planks, 3 ins. by 12 ins., care- 
fully caulked. A temporary floor was built on the base of the 

float, consisting of transverse 
beams, 16 ins. by 16 ins., 
placed 8 ft. apart. A center 
piece, 10 ins. by 16 ins., was 
laid so as to correspond with 
the axis of the tunnel; and 
on each side of it, other 
parallel beams, 16 ins. by 
16 ins., corresponding to each 
center of the circular metal 
lining of the tunnel; the 
beams, longitudinal and transversal, were strongly bolted to- 
gether. The temporary floor was completed by boarding the 
spaces left between the various beams. 

On this float, the upper half of the tunnel was constructed by 
erecting the segments of the metal lining, which were strongly 
supported, so as to prevent any settling or distortion; the con- 
crete was then built up in a large flange with vertical suspension 
rods, four to each bar. The rings of the tunnel were 6 ft. each, 
the weight of each lining being 41,000 lbs., the concrete covering 
618 cubic feet. The second part of the tunnel was 300 ft. long, 
with roof constructed in three sections — two of 90 ft. in length 
each and the third of 84 ft. Each of these sections alternated 
with a smaller section, 12 ft. long, provided with air-locks. The 
shortest of the three sections was the first one set up, and was 
constructed close to the Bronx side of the Harlem River. For 
this purpose the two extreme ends of the section were closed by 
means of steel plates forming diaphragms, built 6 ft. inward, 
thus leaving one ring projecting out at each end. Openings were 
left on the top of these projecting rings for access by divers. The 
exterior of the upper half section of the permanent tunnel was 
filled with water until it was lowered into position. It was 



SUBMARINE TUNNELING 



291 



directed by means of tackles attached to vertical eye-bars, which 
were strongly fixed to the flanges of the springing line of the arch, 
and bolted to the beams of the temporary floor. In this way the 
roof was towed into place, and lowered by means of stone ballast, 
until it rested on the cap-pieces and frames of the pile abutments, 
the sides of the roof remaining just on top of the sheeting-piles 
that formed the sides of the caisson, as shown in Fig. 147. Per- 
fect alignment was obtained by wires strung at each end and 
along the side of the roof, corresponding to points fixed on 
the working platforms and 
sighted with transits. Such 
accuracy was obtained that 
the circumferential flanges 
of the outer 6-ft. ring were 
brought into contact with 
those of the 12-ft. section 
already constructed. A diver 
then entered by the opening 
left in the projecting ring, 
and bolted this section of 
the roof to the preceding one. By removing the iron diaphragm, 
the consecutive sections were united into one. When the diver 
completed his work, the opening was closed up, and compressed 
air used to keep the water out of the box included between the 
roof and the temporary flooring. 

The remaining sections of the tunnel roof were built in the 
same w^ay, until the last abutted against the part of the work 
constructed within the caisson under the high wooden roof on 
the Manhattan side of the river. The following method was 
adopted for the purpose of connecting the few parts of the tunnel 
which had been differently constructed. The diaphragm at the 
end of the last section of the tunnel roof was constructed so as 
to abut against the last circumferential flanges of the iron lining 
without leaving a projecting ring. It was continued above the 
metal and concrete lining of the roof in a rectangular form, and 




Fig. 147. — Showing the Roof of the Caisson 
Formed by the Upper Half of the Tunnel. 



292 



TUNNELING 



of the same height and width as the wooden bulkhead of the 
working-chamber on the Manhattan side of the river. The 
diaphragm was made of riveted plates and angles, with an open- 
ing 20 ins. by 30 ins., bolted so as to be removable at will. The 
diaphragm was of the same height as the roof and was connected 
with a roof-plate to the rangers supporting the thick wooden 
roof. Other steel plates, placed vertically, were riveted to the 
diaphragm and bolted to the caisson. All this work was carried 
on by divers. The wooden bulkhead was cut to the springing- 
hne of the arch; and between the two parts of the tunnel, built- 
by different methods, a bulkhead was placed, made of steel 
plates 14 ins. long, which prevented the entrance of water into 
the working-chamber. 

When the different sections were joined together, and all 
the openings closed and made water-tight, cement-grout was 
poured on the roof, and earth was heaped up to a height of 5 ft. 

The 300 ft. of the roof, resting 
on sheeting-piles and provided 
with diaphragms at the ex- 
treme ends, formed a water- 
tight working-chamber, or cais- 
son, communicating with the 
exterior by means of the shafts 
and air-locks. The lower por- 
tion of the tunnel was built 
under air-pressure. The pile- 
bents were first cut off at the 
plane of the tunnel sub-grade, after which the foundation-bed 
of concrete was laid. The lower segments of the iron Hning were 
then placed in position, and the structure made continuous by 
building up the lateral walls, consisting of concrete (Fig. 148). 
No accidents occurred while building the second part of the 
tunnel. 

The Harlem River tunnel was completed in contract time, 
although the opening of the subway was delayed by difficulties 




Fig. 148. — Showing the Tunnel Completed 
by Building the Lower Half within the 
Caisson. 



SUBMARINE TUNNELING 293 

encountered in tunneling through rock in the borough of the 
Bronx. The writer endeavored to obtain information regarding 
the expense per Hnear foot, but all his efforts were rewarded with 
a general assurance that it proved to be the cheapest method. 

SINKING AND JOINING TOGETHER SECTIONS OF TUNNELS 

BUILT ON LAND. THE SEINE. THE DETROIT 

RIVER TUNNELS. 

In the year 1896, Mr. Erastus Wyman secured a patent for 
building subaqueous tunnels close to the river, by sinking and 
joining together small sections of tunnels previously built on 
land. Each section would have been provided with a long 
vertical tube for the air-lock when compressed air was to be 
admitted to expel the water and permit the construction of the 
lining within the sunken shell. Thus each section of the tunnel 
would have acted as a pneumatic caisson; being, however, an 
improvement on Professor Winkler's suggestion inasmuch as the 
caisson was a portion of the tunnel itself, instead of a simple 
inclosure for facilitating the construction of the shield. Mr. 
Wyman proposed to use this method in the construction of a 
tunnel between South Brooklyn and Stapleton, Staten Island; a 
charter was granted him but the tunnel was never built. 

The Tunnel under the Seine River. — The caisson method of 
building tunnels under water was used at Paris, France, in the 
construction of the Metropolitan Railroad under the Seine River. 

The caissons designed by Mr. L. Chagnaud were for a double 
track line. They were sunk, ends to ends, and formed a portion 
of the tunnel lining which was enveloped by a framework of 
metal embedded in concrete. Built-up frames carried a shell of 
steel plating on the sides, from toes to springing hues, and on 
the sides and roof of the working-chamber. A temporary plate 
diaphragm closed the open ends. This construction formed a 
vessel capable of floating with a very light draft. 

The method of sinking the caissons was as follows : The cais- 
son was erected on the river bank and when completed it was 



294 



TUNNELING 



launched and towed into position between pile stagings which 
served the double purpose of guiding the descent at the beginning 
of the sinking and of forming a working platform. The caisson 
when launched and, consequently, before the cast-iron hning 
had been put in place within it, weighed 280 metric tons; but, 
beyond some difficulty in taking it under the bridges in the way, 
the towing was accomplished without serious trouble. 





i Working \ Chamber 



Fig. 149. — Transversal Section of the Caissons for the Tunnel under the Seine River. 

Previous to placing the caisson in position between the 
stagings, the portion of the river bed it was to rest upon had 
been leveled by dredging. Once in position, the first work was 
the erecting of the cast-iron lining segments within the frame- 
work. Work was then begun by filling the annular space between 
the lining and the shell with concrete; this additional weight 
gradually sunk the caisson to the river bottom. The working 
shafts, made up of steel cylinders, were placed as the sinking 
progressed to this point. 

After the caissons had been sunk to the required place and 
in continuation of one another, a space of nearly 5 ft. was left 
between them. The construction of the tunnel within the bank 



SUBMARINE TUNNELING 



295 



of earth separating the two caissons was as follows : A cofferdam 
was built around this space. It was formed by two diaphragms 
closing the ends of the tunnel, and by two longitudinal walls 
sunk as temporary caissons, one on each side of the tunnel 



SEINE RIVER 

Surface of Wafer 




Working Chamber 
Section' C>"-'A-B ' " 



Caisson No. 4. 




Ene 
^ News. 



Fia. 150. 



Section C-D. 



Caisson No. 5. 
Plan at Joint. 

Showing the Joining of the Caissons at the Pont Mirabeau Tunnel under the 
Seine River. 



^ 



and inclosing their ends. This cofferdam was covered with a 
metal working-chamber whose lower edges rested on top of the 
four walls of the cofferdam. The joints were made tight by 
means of rubber or packed clay. The water in the cofferdam 
was then pumped out, the earth excavated, and the masonry 
built in continuation of the two ends of the tunnel sections. 
The submerged sections of the tunnel which were allowed to 



296 TUNNELING 

remain full of water to render them more stable and to save effort 
in pumping them, were now made dry; the diaphragms were 
removed from the ends of the caisson tunnels and the work made 
continuous. Fig. 149 shows the cross-section of the caissons. 

At the Pont Mirabeau crossing of the Seine, a slightly differ- 
ent method was used, described in ''Eng. News," May 18, 1911. 
The caissons were sunk to the required line and grade with an 
intervening longitudinal space of 15f ins. between two adjoining 
caissons. At each end of this space, which was filled with the 
river marl, was sunk against the edges of the caissons a hollow 
cylinder 20 ins. outside diameter. The interior of these cyl- 
inders was excavated and filled with concrete, thus forming a 
continuous wall on both sides of the two adjoining caissons. 
The earth from the intervening space was then removed and 
concrete deposited from bottom opening tremies up to the level 
of the top of the caisson. After nearly one month the tunnel 
was entered from the shaft and an opening the shape and size 
of the tunnel section cut through the diaphragms of the 15f-in. 
wall and the concrete tunnel lining made continuous between 
the two sections. Fig. 150 shows the method of joining the 
caissons. 

The Detroit River Tunnel.* — With some modifications which 
permitted dispensing with compressed air, the tunnel under the 
Detroit River was built for the Michigan Central Railroad, con- 
necting Detroit with Windsor, Canada. The tunnel is 6625 ft. 
long; of this, however, only 2625 ft. are under the river, while 
the approach on the American side is 2000 ft. long and that on 
the Canadian side, 4000 ft. The tunnel consists of two parallel 
circular tubes 23 ft. in diameter, built up of |-in. steel plate. 
They are placed 26 ft. apart, center to center, and are connected 
by diaphragms at 12-foot intervals. 

Each section of the subaqueous tunnel is approximately 
262 ft. long. There are ten of these sections and an eleventh a 
little over 60 ft. long. These tubes were built at the shipyards 

* Condensed from a paper by B. H. Ryder. 



SUBMARINE TUNNELING 297 

of the Great Lakes Engineering Works at St. Clair, about 30 
miles from Detroit. After the assembling was completed, the 
ends of each tube were closed by temporary wooden bulkheads 
to make them float, and the outside sheathed horizontally with 
heavy timbers bolted to the diaphragms. This sheathing running 
lengthwise of the tube made a form or pocket, into which the 
inclosing jacket of concrete was placed. The sections were then 
launched and towed down to the tunnel side and sunk separately 
in a trench on the river bottom that had been previously dredged 
to receive them. This trench was dug to a width of 50 ft. and 
depth varying from 25 to 50 ft. by clamshell buckets, swung 
from a scow, working to a depth below the water level of 60 to 
90 ft. 

As a foundation for the sections, a grillage was constructed 
on the surface and sunk in place in the trench by derricks swung 
from a scow. The grillage was placed underneath each joint 
between the sections and built up of I-beams imbedded in con- 
crete. This grillage is the width of the trench and about 30 ft, 
long, with posts projecting downward from the four corners, and 
these were seated into the river bottom, by means of pile drivers, 
to the desired grade. 

Then the eleven sections of the tunnel were lowered and con- 
nected, one at a time. By the aid of air tanks placed on each 
section the movement was controlled until the final sinking upon 
the grillage in the trench. This operation called into play the 
greatest engineering skill and ingenuity. When it is considered 
that the current velocity at the river bed is about 2 ft. per second 
and much higher along the surface, some idea can be gained of 
the problems to be overcome. The movement of the enormous 
sections must be absolutely under control. Thirty-five-ton 
blocks of concrete were sunk in the river bottom up and down 
stream to act as anchors, and through them cables were rigged 
and connected back to the hoisting engines on the derrick scows. 
These were prevented from moving by spuds at each corner, 
securely driven into the river bottom at depths sometimes as 



298 



TUNNELING 



great as 90 ft. Controlling cables were also run from the sections 
to the tremie scow to pull one structure close to the adjoining 
section previously sunk, and the divers made the necessary con- 
nection. Fig. 151 shows cross-sections and plans of the tunnel 
as given in ''Eng. Record/' March 2, 1907. 



. 55-8- 




HAUF HORIZONTAL SECTION X-X HALF TOP VIEW 

Fig. 151. — Cross-Sections and Plans of the Detroit River Tunnel. 

Steel masts had been previously attached to each end of the 
sections to enable the engineers on shore to determine the align- 
ment and locate the exact position during the sinking. 

Concrete was then deposited in the pockets, completely sur- 



SUBMARINE TUNNELING 299 

rounding the tubes, forming a solid monolithic structure from 
end to end. 

This was done by means of the tremie process. 

A 32-ft. by 160-ft. scow was equipped with a concrete mixing 
plant and the tremie pipes, three in number, through which the 
concrete was deposited. Each pipe is 12 ins. in diameter, of 
spiral riveted steel, 80 ft. long. These pipes could be raised or 
lowered, reaching from the receiving hoppers on the scow to the 
bottom of the trench. When the pipes were filled with concrete 
and lowered into position, a continuous flow was maintained. As 
fast as the concrete escaped at the bottom end of the pipe it was 
replenished at the top ; this process continuing until the entire 
space surrounding the section was filled to the desired level, and 
under the pressure produced not only by the depth of water 
under which it was submerged, but also by the weight of the long 
column of concrete contained in the tubes. It is interesting to 
note that this is the first time a large amount of concrete has 
been deposited at a depth of 70 ft. by this method, and upon the 
accomplishment of this task in a measure depended the success- 
ful building of the tunnel. 

Inside the tubes was placed a lining of reinforced concrete 
20 ins. thick. Side walls were built up from this ring to provide 
ducts, which carry the electrical cables for the distribution of 
power, lighting, signal and telegraph wires. They also serve to 
provide a footwalk along the side of the tunnel. 

There are cross passages in the tunnel every 200 ft., and 
also various niches for the different equipment needed in connec- 
tion with the signaling, telephone and fire alarm system. The 
tunnel is lighted with 800 16-candle-power incandescent lights. 

The track construction is new. There is no ballast used, 
the ties being laid in concrete. A ditch in the center of each 
track carries the rainfall that will flow down from the summits 
to sumps which are drained by centrifugal pumps. 

One remarkable feature of its construction is that com- 
pressed air was not used in the building of the subaqueous 



300 TUNNELING 

tunnel, but it was necessary in building the approach tunnels. 
This is contrary to the usual program where compressed air is 
required in subaqueous work, and not ordinarily used in approach 
or land tunnel construction. 

The trains are operated by very heavy electric locomotives, 
operated by the third-rail system. 

The tunnel was constructed under the supervision of W. S. 
Kinnear, Chief Engineer of the Detroit River Tunnel Co. ; Butler 
Bros, of New York were the general contractors. 



ACCIDENTS AND REPAIRS IN TUNNELS 301 



CHAPTER XXII. 

ACCIDENTS AND REPAIRS IN TUNNELS DURING 
AND AFTER CONSTRUCTION. 



In the excavation of tunnels it often happens that the dis- 
turbance of the equilibrium of the surrounding material by the 
excavation develops forces of such intensity that the timbering 
or lining is crushed and the tunnel destroyed. To provide 
against accidents of this kind in a theoretically perfect manner 
would require the engineer to have an accurate knowledge of 
the character, direction and intensity of the forces developed, 
and this is practically impossible, since all of these factors differ 
with the nature and structure of the material penetrated. The 
best that can be done, therefore, is to determine the general 
character and structure of the material penetrated, as fully as 
practicable, by means of borings and geological surveys, and 
then to employ timbering and masonry of such dimensions and 
character as have withstood successfully the pressures devel- 
oped in previous tunnels excavated through similar material. 
If, despite these precautions, accidents occur, the engineer is 
compelled to devise methods of checking and repairing them, 
and it is the purpose of this chapter to point out briefly the 
most common kinds of accidents, their causes, and the usual 
methods of repairing them. 

Accidents During Construction. — Accidents may happen both 
during or after construction, but it is during construction, when 
the equilibrium of the surrounding material is first disturbed, 
and when the only support of the pressures developed is the 
timber strutting that they most commonly occur. 



302 TUNNELING 

Causes of Collapse. — Collapse in tunnels may be caused : (1) 
by the weight of the earth overhead, which is left unsupported 
by the excavation ; (2) by defective or insufficient strutting ; 
and (3) by defective or weak masonry. 

(1) The danger of collapse of the roof of the excavation is 
influenced by several conditions. One of these is the method 
of excavation adopted. It is obvious that the larger the 
volume of the supporting earth is, which is removed, the 
greater will be the tendency of the roof to fall, and the more 
intense will be the pressures which the strutting will be called 
upon to support. Thus the English and Austrian methods of 
tunneling, where the full section is excavated before any of the 
lining is placed, and where, as the consequence, the strutting 
has to sustain all of the pressures, present more likehhood of 
the roof caving in than any of the other common methods. 

The character and structure of the material penetrated also 
influence the danger of a collapse. A loose soil with little 
cohesion is of course more likely to cave than one which is 
more stable. Rock where strata are horizontal, or which is 
seamy and fissured, is more likely to break down under the roof 
pressures than one with vertical strata and of homogeneous 
structure. Soft sod containing boulders whose weight develops 
local stresses in the roof timbering is likely to be more danger- 
ous than one which is more homogeneous. A factor which 
greatly increases the danger of collapse, especially in soft soils, 
is the presence of water. This element often changes a soil 
which is comparatively stable, when dry, into one which is 
highly unstable and treacherous. The liability of the material 
to disintegration by atmospheric influences and various other 
conditions, which will occur to the reader, may influence its 
stability to a dangerous extent, and result in collapse. 

(2) Collapse is often the result of using defective or insuf- 
ficient strutting. Of course, in one sense, any strutting which 
fails under the pressures developed, however enormous they 
may be, can be said to be insufficient, but as used here the term 



ACCIDENTS AND REPAIRS IN TUNNELS 303 

means a strutting with an insufficient factor of safety to meet 
probable increases or variations in pressure. Insufficient strut- 
ting may be due to the use of too light timbers, to the spacing 
of the roof timbers too far apart, to the yielding of the founda- 
tions, to insufficient bearing surface at the joints, etc. Collapse 
is often caused by the premature removal of the strutting dur- 
ing the construction of the masonry. The masons, to secure 
more free space in which to work, are very likely, unless 
watched, to remove too many of the timbers and seriously 
weaken the strutting. 

(3) The third cause of collapse is badly built masonry. 
Poor masonry may be due to the use of defective stone or brick, 
to the thinness of the lining, to poor mortar, to weak centers 
which allow the arch to become distorted during construction, 
to poor bonding of the stone or bricks, to the premature 
removal of the centers, to driving some of the roof timbers 
inside it, etc. 

Prevention of Collapse. — Tunnels very seldom collapse with- 
out giving some previous warning of the possible failure, and 
also of the manner in which the failure is likely to occur. 
From these indications the engineer is often able to foresee the 
nature of the danger and take steps to check it. The danger 
may occur either during excavation or after the lining is built. 
During excavation the danger of collapse is indicated before- 
hand by the partial crushing or deflection of the strutting tim- 
bers. If the timbers are too light or the bearing surfaces are 
too small, crushing takes place where the pressures are the 
greatest, and the timbers bend, burst, or crack in places, and the 
joints open in other places. The remedy in such cases is to in- 
sert additional timbers to strengthen the weak points, or it may 
be necessary to construct a double strutting throughout. 
When the distance spanned by the roof timbers is too great, 
failure is generally indicated by the excessive deflection of 
these timbers, and this may often be remedied by inserting 
intermediate struts or props. In some respects the best remedy 



304 TUNNELING 

under any of these conditions is to construct the masonry as 
soon as possible. 

When collapse is likely to occur after the masonry is com- 
pleted, its probability is generally indicated by the cracking 
and distortion of the lining. A study of the cause is quite 
likely to show that it is the percolation of water through the 
material surrounding the lining which causes cavities behind 
the lining in some places, and an increase of the pressures in 
other places. When it is certain that this water comes from 
the surface streams above, these streams may often be diverted 
or have their beds lined with concrete to prevent further perco- 
lation. When percolating water is not the cause of the trouble, 
a usually efficient remedy is to sink a shaft over the weak point, 
and refill it with material of more stable character. These, 
and the remedies previously suggested, are designed to prevent 
failure without resorting to reconstruction. When they or 
similar means prove insufficient, reconstruction or repairs have 
to be resorted to. 

Repairing Failures. — Tunnels may collapse in several ways : 
(1) The front and sides of the excavation may cave in; (2) 
the floor or bottom may bulge or sink ; (3) the roof may fall 
in; (4) the material above the entrances may slide and fill 
them up. 

(1) One of the most common accidents is the caving of the 
front and sides of the excavation. This may often be prevented 
by taking care that the face of the excavation follows the natu- 
ral slope of the material instead of being more or less nearly 
vertical. When, however, caving does occur it may usually 
be repaired by removing the fallen material, strongly shoring 
the cavity, and filling in behind with stone, timber, or fascines. 

(2) The bulging or rising of the bottom of the tunnel may 
usually be considered as a consequence of the squeezing together 
of the side walls. It usually occurs in very loose soils, and is 
chiefly important from the fact that the reconstruction of the 
side walls is made necessary. The sinking of the tunnel bot- 



ACCIDENTS AND REPAIRS IN TUNNELS 305 

torn is a more serious occurrence. It seldom happens unless 
there is a cavity beneath the floor, due either to natural causes 
or to the fact that mining operations have gone on in the hill 
or mountain penetrated by the tunnel. When the bottom of 
the tunnel sinks, three cases may be considered : (a) when the 
sinking is limited to the middle of the tunnel floor ; (6) when 
only a portion of the foundation masonry is affected ; and, ((?) 
when the entire lining is disturbed. In the first case repairs 
are easily made by filling in the cavity with new material. In 
the second case the unimpaired portion of the masonry is tem- 
porarily supported by shoring while the injured portion is re- 
moved and rebuilt on a firm foundation. The remaining cavity 
is then filled. In the case of the complete failure of the lining, 
the method of repairing employed when the roof falls, and 
described below, is usually adopted. 

(3) The most dangerous of all failures is the falling of the 
tunnel roof. In such casualties two cases may be considered : 
(a) When the falling mass completely fills the tunnel section, 
and (5) when it fills only a portion of the section. 

When the whole section is filled by the fallen material, the 
problem may be considered as the excavation of a new tunnel 
of short length inside the old tunnel, and under rather more 
difficult conditions. The first task, particularly if men have 
been imprisoned behind the fallen material, is to open com- 
munication through it between the two uninjured portions of 
the tunnel. It is advisable to do tliis even when there is no 
danger to life because of imprisoned workmen, since it enables 
the work of repairing to be conducted from both directions. 
The excavation of a passageway through the fallen material 
is rendered difficult, both because the fallen material is of an 
unstable character, and also because it is usually filled with the 
hning masonry, timbering, etc. When, therefore, the accident 
has happened before the full section of the original material 
has been removed, the first heading or drift is driven through 
this original material rather than through the fallen debris. 



306 



TUNNELING 



Any of the regular soft-ground methods of tunneling may be 
employed, but it is usually better to select one which allows 
the masonry to be built with as little excavation as possible at 
first. For this reason the German method of tunneling is par- 
ticularly suited to repair work of this nature. The Belgian 
method may also be used to advantage, particularly w^hen the 
caving extends to the surface of the ground above, and the 
upper portion of the debris is, therefore, practically the same 
material as that through which the original tunnel was driven. 
The greatest defect of the Belgian method for making repairs 
is that the roof arch is supported by a rather unstable mass of 







Fig. 152.— Tunneling tlirougli Caved Material by Heading. 

mingled earth, stone, and timber, which constitutes the bottom 
layer of the fallen material. The method of strutting the work 
when the German or Belgian method is used is shown by Fig. 
152. It sometimes happens that the fallen debris is so un- 
stable that it will not carry safely the arch masonry in the 
Belgian method or the strutting in the German method, and in 
these cases one of the full-section methods of excavation is 
usually adopted. The nature of the strutting employed is 
shown by Fig. 153. When the section has been opened and 
the new masonry built, great care should be taken to fill the 
ca\dty behind the masonry with timber or stone ; and should 



ACCIDENTS AND REPAIRS IN TUNNELS 



307 



the disturbance reach to the ground surface it is often a good 
plan to sink a shaft through the disturbed material, and fill it 
with more stable material. 







Fig. 153. —Tunneling through Caved Material by Drifts. 

When the fallen debris fills only a part of the section, the 
first thing to provide against is the occurrence of any further 
caving ; and this is usually done by building a protecting roof 
above the line of the future roof masonry. Figs. 154 and 155 





Figs. 154 and 155. —Filling in "Roof Cavity Formed by Falling Material, 

show two methods of constructing this temporary roof, which 
it will be noticed is filled above with cordwood packing. As 
soon as the temporary roof is completed, the lining masonry is. 
constructed. 



308 



TUNNELING 



(4) Landslides which close the tunnel entrance are repaired 
in a variety of ways. Fig. 156 shows a common method of 
preventing the extension of a landslide which has been started 




Fig. 156. —Timbering to Prevent Landslides at Portal. 

by the excavation for the entrance masonry. Fig. 157 shows a 
method often adopted when the slope is quite flat and the 
amount of sliding material is small. It consists essentially of 
removing the fallen material and building a new portal farther 
back ; that is, the open 
cut is extended and the 
tunnel is shortened. 
When the amount of 
the sliding material is 
very large, the contrary 
practice of lengthening 
the tunnel and shorten- 
ing the open cut, as 
shown by Fig. 158, 
may be adopted. 

Accidents After Construction. — Accidents after the comple- 
tion of the tunnel may be divided into two classes: first, 
those which entirely obstruct the passage of trains, of which the 
collapse of the roof is the most common ; and second, those which 
allow traffic to be continued while the repairs are being made, 




Fig. 157. 



•Shortening Tunnel Cruslied by Landslide 
at Portal. 



ACCIDENTS AND REPAIRS IN TUNNELS 309 

such as the bulging inward of a portion of the lining without 
total collapse. In the first case the first duty of the engineer 
is to open communication through the fallen debris, so 
that passengers at least may be transferred from one part of the 
tunnel to the other and proceed on their way. This is done 
by driving a heading, and strongly timbering it to serve as a 
passageway. If the tunnel is single tracked this heading is 
afterwards enlarged until the whole section is opened. In 
double-track tunnels the method generally adopted is to open 
first one side of the section and timber it strongly, so as to clear 
one track for traffic. While the trains are run- 
ning through this temporary passageway the 
other half of the section is opened and re- 
paired ; the traffic is then shifted to the 
new permanent track, and the temporary 
structure first employed is replaced 
with a permanent 
When the accident is 
that the repairs can b 
made without ob- 
structing traffic en- 

tirely, various -p^^ jgg — Extending Tunnel through Landslide at Portal. 

modes of procedure 

are followed. In all cases great care has to be exercised to 
prevent accident to the trains and to the tunnel workmen. 
The work should be done in small sections so as to disturb as 
little as possible the already troubled equilibrium of the soil ; 
the strutting should be placed so as to give ample clearing 
space to passing trains, and the trains themselves should be run 
at slow speeds past the site of the repairs. To illustrate the 
two kinds of accidents and the methods of repairing them, 
which have been mentioned, the accidents at the Giovi tunnel 
in Italy and at the Chattanooga tunnel in America have been 
selected. 

Giovi Tunnel Accident. — In September, 1869, at a point about 




310 TUNNELING 

220 ft. from the south portal of the Giovi tunnel, a disturbance 
of the masonry linmg for a length of about 52 ft. was observed. 
Accurate measurements showed that the lining was not sym- 
metrical with respect to the vertical axis of the sectional profile. 
It was concluded that omng to some disturbance of the sur- 
rounding soil unsymmetrical vertical and lateral pressures were 
acting on the masonry. Close watch was kept of the dis- 
torted masonry, which for some time remained unchanged 
in position. In 1872, however, new crevices were observed 
to have developed, and shortly afterwards, in January, 1873, 
the injured portion of the masonry caved in, obstructing 
the whole tunnel section. The fallen material consisted 
chiefly of clay in a nearly plastic state. The surface of the 
ground above was observed to have settled. Investigation 
showed also that the cause of the caving was the percolation of 
water from a nearby creek. The water had soaked the ground, 
and decreased its stability to such an extent that the masonry 
lining was unable to withstand the increased vertical and lateral 
pressures. 

The mode of procedure decided upon for repairing the 
damage was : (1) To open at least one track for the temporary 
accommodation of traffic ; (2) To remove permanently the causes 
which had produced the collapse ; (3) To build a new and 
much stronger lining. Close to the western side wall, which 
was still standing, the debris was removed, and the opening 
strongly strutted in order to allow the laying of a single 
track to reestablish communication. At the same time a shaft 
was sunk from the surface above the caved portion of the tunnel, 
for the double purpose of facilitating the removal of the 
fallen material and of affording ventilation. The depth of the 
surface above the tunnel was 41.6 ft., which made the construc- 
tion of the shaft a comparatively easy matter. The shaft itself 
was 6^ ft. wide and 18 ft. long, with its longer dimensions parallel 
to the tunnel, and it was lined with a rectangular horizontal 
frame and vertical-poling board construction. After tem- 



ACCIDENTS AND REPAIRS IN TUNNELS 311 

porary communication had been opened on the western track of 
the tunnel, the remainder of the fallen earth was removed and 
the excavation strutted. The new masonry lining was then 
built. 

To remove permanently the cause of the cave-in, which was 
the percolation of water from a close-by stream, this stream was 
diverted to a new channel constructed with a concrete bed and 
side walls. 

The failure of the original lining occurred by cracks develop- 
ing at the crown, haunches, and springing lines. The new lining 
was made considerably thicker than the original lining, and at 
the points where failure had first occurred in the original arch 
cut-stone voussoirs were inserted in the brickwork of the new 
arch as described in Chapter XIII. 

Chattanooga Tunnel. — The Western & Atlantic Ry. passes 
through the Chattanooga mountains by means of a single-track 
tunnel 1,477 ft. long, constructed in 1848-49. The lining con- 
sisted of a brickwork roof arch and stone masonry side walls. 
After the tunnel had been opened to traffic, this lining bulged 
inward at places, contracting the tunnel section to such an ex- 
tent that it was decided to reconstruct the distorted portions. 
After careful surveys and calculations had been made, it was 
decided to take down and reconstruct about 170 ft. of the 
lining. 

Owing to contracted space in the tunnel, it was necessary 
to remove all men, tools, and material, whenever trains were 
to pass through ; and in order to do this a work-train of 
three cars was fitted up with necessary scaffolds, and supplied 
with gasoline torches for lighting purposes. Mortar was mixed 
on the cars, and all material remained on them until used. 
Debris torn out of the old wall was loaded on the cars, and 
hauled to the waste dump. A siding was built near the West 
end of the tunnel for the use of this train, and a telephone sys- 
tem was installed between the entrances and the working-train. 
On account of the contracted working-space and the greater 



312 TUNNELING 

ease with which brick could be handled, it was decided to re- 
build the walls out of brick instead of stone. 

In tearing out the old wall a hole was first cut through the 
three bottom courses of the arch and gradually widened. When 
the opening became four or five feet long, a small jack was 
placed near the center of it and brought to a bearing against 
the arch to sustain it. After cutting the opening to a length 
of from 7 to 10 ft. depending on the stability of the earth 
backing, the jack was removed and a piece of 8x16 in. timber 
placed under the arch and brought up to a bearing with jacks. 
One end of the timber rested on the old wall, the other on a seat 
built into the adjoining section of new wall. Wedges were 
then driven under the ends of timber and the jacks removed. 
With this timber in place, the old wall could be taken down 
with ea§e, the only trouble being that small stones and earth 
fell in from above and behind the arch. This was obviated 
by placing a 2 in. plank across the opening and just back of 
the 8x16 in. timber. At several points, however, the earth 
backing was saturated with water, and it became necessary to 
put in lagging as the old wall was removed. This timbering 
would be taken out as the new work was built up. 

A suitable foundation for the new wall was secured at a 
depth from 2 to 4 ft., and a concrete footing was used. The 
section of the new wall was then built up as near as possible to 
the 8x16 in. timber; the timber was then removed and the 
new wall built up and keyed under the arch. 

The new wall had a minimum width of 2^ ft. at the top, 
and 4 ft. at the base of rail, and was provided with weep holes 
at intervals. To facilitate matters, work was carried on simul- 
taneously at two or three different places, the intention being 
to get one place torn out and ready for the bricklayers by the 
time they completed a section of the new wall at another 
place. 

In rebuilding the arch, sections extending from the spring- 
ing line up as far as was necessary to obtain the desired clear- 



ACCIDENTS AND REPAIRS IN TUNNELS 313 

ance, and from 2i to 4 ft. in length, were removed. Near the 
sides, the earth above the arch was a stiff clay, which was self- 
sustaining; but near the center there occurred a stratum of 
gravel and clay saturated with water. This gave considerable 
trouble, falling through almost continuously until timbering 
could be placed. One end of this timber rested on the old 
arch, the other on the adjoining section of the new work. As 
the new work was to be set 6 to 13 ins. back from the old, it 
was necessary to block up this distance on top of the old arch, 
to carry the end of the lagging timber, in order that the timber 
should be clear of the new arch. 

Owing to the small clearance between the car roof and the 
arch, a special form of centering was required, one that would 
occupy as small space as possible. Bar iron 1 in. thick, 4 ins. 
wide, and 20 ft. long was curved to a radius of 6i ft., and on 
the underside of this was riveted a 6-in. plate i in thick. This 
plate projected 1 in. on the sides of the centering, and carried 
the ends of the 1 in. boards used for lagging. The rivets were 
counter-sunk on the outside of the centering to present a smooth 
surface next the arch. 

In keying up a section of the new work, a space about 18 ins. 
square had to be left open for the use of the workmen. As 
soon as the next section had been torn out, this space was built 
up. In building up the last section, this space had to be filled 
from below, which proved to be a tedious undertaking. The 
opening was gradually reduced to a size of 10 x 18 in., and the 
top ring then completed and keyed up, the adhesion of mortar 
holding the bricks in place until the key could be driven home. 
The next ring was treated in a similar manner, and so on to the 
face ring. Altogether 412 lin. ft. of the walls and 178 lin. ft. 
of the arch were taken down and rebuilt, amounting in all to 
607 cu. yds. of masonry at the total cost of 17,440, or about 
112.25 per cu. yds. 

The regular trains arrived so frequently at the tunnel that 
slightly over two hours was the longest working-time between 



314 TUNNELING 

any two trains, and usually less than one hour at a time was all 
that it could be worked. In addition to the regular trains, a 
large number of extra trains, moving troops, had to be accom- 
modated. Work was in progress eight months, and during that 
time there was no delay to a passenger train. The repairs were 
completed in August, 1899. The work was under the direction 
of Mr. W. H. Whorley, engineer of the Western & Atlantic 
R. R., and foreman of construction, A. H. Richards. A recent 
examination failed to reveal any sign of settlement cracks at the 
junction points of the new and old work. 



RELINING TIMBER-LINED TUNNELS WITH MASONRY 315 



CHAPTER XXIII. 

RELINING TIMBER-LINED TUNNELS WITH 
MASONRY. 



The original construction of many American railway tunnels 
with a timber lining to reduce the cost and hasten the work has 
made it necessary to reline them, as time has passed, with some 
more permanent material. In most cases the work of removing 
the old lining and replacing it with the new masonry has had 
to be done without interfering with the running of trains, and a 
number of ingenious methods have been developed by engineers 
for accomplishing this task. Three of these methods which 
have been employed, respectively, in relining the Boulder 
tunnel on the Montana Central Ry., in Montana, the MuUan 
tunnel on the Northern Pacific Ry., in Montana, and the Little 
Tom tunnel on the Norfolk & Western R. R., in Virginia, have 
been selected as fairly representative of this class of tunnel 
work. 

Boulder Tunnel. — This tunnel penetrates a spur of the main 
range of the Rocky Mountains, at an elevation at the summit 
of grade of 5,454 ft., and is 6,112 ft. in length. Its alignment is 
a tangent, with the exception of 150 ft. of 30' curve at the 
north end. The material penetrated is blue trap-rock with 
seams for 4,950 ft. from the north end, and syenitic boulders 
with the intervening spaces filled with disintegrated material 
for the remaining 1,160 ft. The dimensions and character of 
the old timber lining and of the new masonry lining replacing 
it are shown in Figs. 141 and 142. 

The form of masonry adopted consisted of coarse rubble side 
walls of granite, 13 ft. 8 ins. high, and generally 20 ins. thick, 



316 



TUNNELING 



with a full center circular arch of four rings of brick laid in 
rowlock form. When greater strength was needed the thick- 
ness of the side walls was increased to 30 ins. and that of the 
arch to six rings of brick. 

The first plan adopted in putting in the masonry was to 
remove all the timbering ; but owing to the large number of 
falls and slides this was abandoned, and the plan followed was to 
leave in the three roof segments of the timbering with the over- 
lying cord-wood packing and debris. In carrying on the work 
the first step was to remove the side timbers. This was done 
by supporting the roof timbers, as shown in Fig. 159 ; that is, 
the first and fourth arch rib of an 8-ft. section containing four 




Cross Sertion. 



Uinaitudinal Section. 

Cross Section. 

Figs. 159 and 160.— Relining Timber-Lined Tunnel. 



Cross Section. 



arch ribs were supported by temporary posts. The intermedi- 
ate arch ribs were supported against the downward pressure by 
6 X 6 in. timbers, extending from the side ribs near the tops 
of the temporary posts to the opposite sides of the intermediate 
roof segments, as shown in the longitudinal section. Fig. 160. 
To resist the pressure from the sides, 4 X 6 in. braces were 
placed across the tunnel from near the center of the intermedi- 
ate segments to the upper ends of the hip segments, as shown 
in the cross-section. Fig. 159. The hip segments were then 
sawed off below the notch, and the side timbering removed and 
the masonry built. 

The stone was conveyed into the tunnel on flat cars, and laid 
by means of small derricks located on the cars. Two derricks 



EELINING TIMBER-LINED TUNNELS WITH MASONRY 317 



were used, one for each side wall, and the work on both walls 
was carried on simultaneously. 

The arch was built upon a centering, the ribs of which were 
5i ins. less in diameter than the distance between the side 
walls, so as to permit the use of 2| ins. lagging. Each center 
had three ribs, made in 1-in. or 2-in. board segments, 10 ins. thick 
and 14 ins. deep. These ribs were mounted on frames, which 
followed the opposite walls, and were 4 ft. apart, making the 
total length of the center out to out about 9 ft. The frames, 
upon which the ribs were supported, are shown in Fig. 161. 
As will be seen, they were mounted on dollys to enable the 
center to be moved from one section to another. Jacks were 

used to raise and lower 
the center into its proper 
position. 

The arch was built up 
from the springing lines 
on both sides at the same 
time, four masons being 
employed. The rings 
were built beginning with 
the intrados, which was 
brought up, say, a dis- 
tance of about 2 ft. from the springing line. Then the back of 
the ring was well plastered with from | in. to i in. of mortar, 
and the second ring brought up to the same height and 
plastered on the back, and so on until the last ring was laid. 
After bringing the full width of the arch up some distance, 
new laggings were placed on the ribs for an additional height 
of 2 ft. and the same process was repeated. All the space 
between the extrados of the masonry arch and the old lining 
was compactly filled with dry rubble. When high enough 
so that the hip segments had a foot or more bearing on the 
masonry the segments were securely wedged and blocked up 
against the brickwork, and the longitudinal 4 X 6 in. timbers 




Cross Section. 



longitudinal Section. «»«• 
Fig. 161.— Relining Timber-Lined Tunnel, 
Great Northern Ry. 



318 



TUNNELING 



removed. The remaining space was now clear for completion 
of the arch, and both sides were brought up until there was 
not sufficient space for four masons to work, when the keying 
was completed by two masons beginning at the completed and 
working back toward the toothed end. The brickwork was 
built from the top of a staging-car. 

In a few instances where slides occurred after the removal 
of the slide timbering, the method of re timbering the tunnel 
shown in Fig. 162 was adopted. Two side drifts were first 
run 2i ft. wide by 4 ft. high, and the plate timbers placed in 
position and blocked. Cross drifts were then run, and the roof 
segments placed, and the core down to the level of the bottoms 
of the side drifts taken 
out. The lower wall 
plates were then placed 
and the hip segments 
inserted. The bench 
was then taken down 
by degrees, the side 
plates being held by 
jacks, and the posts 
placed one at a time. 
As the masonry at the 
points where slides occur consists of 30-in. walls and six-ring 
arch, the timbering was 22 ft. wide in the clear, with other 
dimensions as shown in Fig. 162. 

Only a single crew of brick and stone masons was employed. 
In order to prepare the sections for these masons it was 
necessary to have timber and trimming crews at work through- 
out the whole day of 24 hours, so that an engine and two train 
crews were in constant attendance. The single mason crews 
were able to complete 8 ft. of side wall and arch in 24 hours. 
The number of men actually employed at the tunnel was 35. 
This included electric-light maintenance, and all other labor 
pertaining to the work. The tunnel was lighted by an Edison 




Cross Section 



Fig. 162. 



Longitudinal Section. 
Relining Timber-Lined Tunnel, 
Great Northern Ey. 



RELINING TIMBER-LINED TUNNELS WITH MASONRY 319 



dyiiamo of 20 arc light capacity, one arc light being placed on 
each side of the tunnel at all working-places. Each lamp 
carried a coil of wire 20 or 30 ft. long to allow it to be shifted 
from place to place without delay. 

Mullan Tunnel. — This tunnel is 3,850 ft. long, and crosses 
the main range of the Rocky Mountains, about 20 miles 
west of Helena, Mont. The tunnel is on a tangent throughout, 
and has a grade of 20 % falling toward the east. The summit 

of the grade, west of the tun- 
nel, is 5,5^8 ft. above sea 
level, and the mountain above 
the line of the tunnel rises 
to an elevation of 5,855 ft. 
Owing to the treacherous 
nature of the material through 
which the tunnel passed, it 
had been a constant menace 
to traffic ever since its con- 
struction in 1883, and numer- 
ous delays to trains had been 
caused by the- falls of rock 
and fires in the timber lin- 
ing. For these reasons it was 
finally decided to build a per- 
manent masonry lining, and 
work on this was begun in July, 1892. 

The original timbering consisted of sets spaced 4 ft. apart 
c. to c, with 12 X 12 in. posts supporting wall plates, and a 
five-segment arch of 12 x 12 in. timbers joined by li-in. 
dowels. The arch was covered with 4-in. lagging, and the 
space between this and the roof was filled with cordwood. 
Except where the width had been reduced by timbering placed 
inside the original timbering to increase the strength, the clear 
width was 16 ft., and the clear height 20 ft. above the top of 
the rail. Fig. 163 shows the timbering and also the form 




Permanent Work 



Fig. 163. — Reliuing Timber Lined Tunnel, 
Great Northern Ry. 



320 



TUNNELING 



of masonry lining adopted. The side walls are of concrete and 
the arch of brick. This new masonry, of course, required the 
removal of all the original timbering. The manner of doing 
this work is as follows : A 7-ft section, A B, Fig. 164, was first 
prepared by removing one post and supporting the arch by 
struts, aS' S. After clearing away any backing, and excavating for 
the foundation of the side wall, two temporar}^ posts, F F, were 
set up, and fastened by hook bolts. Fig. 146, X, and a lagging 
was built to form a mold for the concrete. Several of these 
7-ft. sections were prepared at a time, each two being sepa- 
rated by a 5-ft. section of timbering. 




^ 



f' F 



LassM. 



F 



1 


1 


r 

1 


^ 


m 


^ 




Uiqqmq 

_ ,, , _ 




~I 


-" "- 


''■r" 



With Wall.Plate. _ Wirtiout Wojl Plate. 

SecHon ,wHh Concrete Osr^ tongitudinal Sectiorx. 

Fig. 164. — Construction of Centering Mullan Tunnel. 

The mortar car was then run along, and enough mortar 
(1 cement to 3 sand) was run by the chute into each section 
to make an 8-in. layer of concrete. As the car passed along 
to each section, broken stone was shoveled into the last preced- 
ing section until all the mortar was taken up. The walls were 
thus built up in 8-in. layers, and became hard enough to sup- 
port the arches in about 10 to 14 days. The arches were then 
allowed to rest on the wall, and the posts of the remaining 5-ft. 
sections were removed, and the concrete wall built up in the 
same way as before. 



RELINING TIMBER-LINED TUNNELS WITH MASONRY 321 



The average progress per working-day was 30 ft. of side 
wall, or about 45 cu. yds. ; and the average cost, including all 
work required in removing the timber work, train service, lights 
and tools, engineering and superintendence, and interest on 
plant, was |8 per cubic yard. 

The centering used for putting in the brick arches is shown 
in Fig. 165. From 3 ft. to 9 ft. of arch was put in at a time, 
the length depending upon the nature of the ground. To re- 
move the old timber arch, one of the segments was partly sawed 
through; and then a small charge of giant powder was exploded 

in it, the resulting debris, 
cordwood, rock, etc., being 
caught by a platform car ex- 
tending underneath. From 
this car the debris was re- 
moved to another car, which 
conveyed it out of the tunnel. 
The center was then placed 
and the brickwork begun, the 
cement car shown in Fig. 164 
being used for mixing the 
mortar. The size of the 
bricks used was 2^ + 2^ + 9 
ins., four rings making a 20- 
in. arch and giving 1.62 cu. yds. of masonry in the arch per 
lin. ft. of tunnel. The bricks were laid in rowlock bond, two 
gangs, of three bricklayers and six helpers each, laying about 12 
lin. ft. per day. The brickwork cost about |17 per cu. yd. 
The total cost of the new lining averaged about |50 per lin. ft. 
Little Tom Tunnel. — The tunnel has a total length of 1,902 
ft., but only 1,410 ft. of it were originally hned with timber. 
This old timber lining consists of bents spaced 3 ft. apart, and 
located as shown by the dotted lines in the cross-section. Fig. 
166. Instead of renewing this timber, it was decided to replace 
it with a brick lining. Although the tunnel was constructed 




Fig. 165.— Centering Mullan Tunnel. 



322 



TUNNELING 




RELINTNG TIMBER-LINED TUNNELS WITH MASONRY 323 

through rock, this rock is of a seamy character, and in some 
portions of the tunnel it disintegrates on exposure to the air. 
In removing tlie timber to make place for the new lining some 
of the roof was found close to the lagging, but often also con- 
siderable sections siiowed breakages in the roof extending to a 
height varying from 1 ft. to 12 ft. above the upper side of the 
timbering. This dangerous condition of the roof made it neces- 




Fig. 167 — flelining Timber-Lined Tunnel, Norfolk and Western Ky. 



sary that only a small section of the timber lining should be 
removed at one time. It made it necessary, also, that the brick 
arch should be built quickly to close this opening, and finally 
that all details of centers, etc., should be arranged so as to 
furnish ample clearance to trains. The accompanying illustra- 
tions show the solution of the problem which was arrived at. 
Referring to the transverse and longitudinal sections shown 



324 TUNNELING 

by Fig. 166, it will be seen that two side trestles were built to 
carry an adjustable centering for the roof arch. Two sections 
of these trestles and centerings were used alternately, one being 
carried ahead and set up to remove the timbering while the 
masons were at work on the other. The manner of setting up 
and adjusting the trestles and centerings is shown by Fig. 148 
and also by Fig. 167, which is an enlarged detail drawing of 
the set screw and rollers for the centering ribs. The following 
is the bill of material required for one set of trestles and one 
center : 

Trestles : 

Caps and sills 8 pieces 8x8 ins. x 20 ft. 

Posts . 18 " 8 X 8 " X 11 " 

Braces 16 " 6x 4 " x 7" 

Centerings : 

Ribs 27 " 2 X 18 " X 7 " 

Bracing 12 " 2 x 8 " x 7 " 

Support to crown lagging 2 " 6 x 6 " x 10 " 

Crown lagging 20 " 3x 6 " X 2" 

Side lagging 30 " 3 x 6 " x 10 " 

Side strips 2 " 2 x 12 " x ^ " 

Blocking for rollers 1 " 5 x 8 " x 12 " 

6 screw and roller castings complete with bolts and lever ; 114 
bolts i-ins. in diameter ; 7? U. H. hexagonal nut and 2 cast washers 
each. 

With this arrangement the progress made per day varied 
from 2 lin. ft. to 3 lin. ft. of lining complete. By work com- 
plete is meant the entire lining, including stone packing between 
the brickwork and the rock. On Feb. 23, 1900, 363 ft. of lin- 
ing had been completed, at a cost of |33.50 per lin. ft. This 
cost includes the cost of removing the old timber, the loose rock 
above it, and all other work whatsoever. 



VENTILATION AND LIGHTING DURING CONSTRUCTION 325 



CHAPTER XXIV. 

THE VENTILATION AND LIGHTING OF TUN= 
NELS DURING CONSTRUCTION. 



VENTILATION. 

In long tunnels, especially when excavated in hard rock, 
proper ventilation is of great importance, because the air cannot 
be easily renewed, and the amount of oxygen consumed by 
miners horses and lamps during construction is very large. 
The gases produced by blasting also tend to fill the head of ex- 
cavation with foul air. Pure atmospheric air contains about 
21 % of oxygen and only 0.04 % of carbonic acid ; when the 
latter gas reaches 0.1 %, the fact is indicated by the bad odor; 
at 0.3 % the air is considered foul, and when it reaches 0.5 ^o it 
is dangerous. It is generally admitted that the standard of 
purity of the air is when it contains 0.08 % of carbonic acid. 

A large quantity of carbonic acid in the air is easily detected 
by observing the lamps, which then give out a dim red light 
and smoke perceptibly ; the workmen also suffer from headache 
and pains in the eyes, and breathe with difficulty. Naturally, 
miners cannot easily work in foul air and, therefore, make very 
slow progress. It is, therefore, to the interest of the engineer to 
afford good ventilation, not only because of his duty to care for 
the safety and health of his men, but also for reasons of econ= 
omy, so that the men may work with the greatest possible ease, 
thus assuring the rapid progress of the work. 

It would be impossible to change completely the atmosphere 
inside a tunnel, as the gases developed from blasting will pene- 
trate into all the cavities and gather there, but the fresh air 



326 TUNNELING 

carried inside by ventilation has a very small percentage of car- 
bonic acid, mixes with that which contains a greater quantity, 
and dilutes it until the air reaches the standard of purity. We 
have not here considered the gases developed from the decom- 
position of carboniferous and sulphuric rocks, which may be 
met with in some tunnels, and which render ventilation still 
more necessary. Tunnels may be ventilated either by natu- 
ral or artificial means. 

Natural Ventilation. — It is well known that if two rooms of 
different temperatures are put in communication with each 
other, e.g., by opening a door, a draft from the colder room will 
enter the other from the bottom, and a similar draft at the top, 
but with a contrary direction, will carry the hot air into the 
colder room, thus producing perfect ventilation, until the two 
rooms have the same temperature. Now, during the construc- 
tion of tunnels the temperature inside may be considered as 
constant, or independent of the outside atmospheric variations ; 
hence during summer and winter, there will always be a draft 
affording ventilation, owing to the difference of temperature in- 
side and outside the tunnel. In winter time the cold air out- 
side will enter at the bottom of the entrances and headings, or 
along the sides of the shafts, and the hot air will pass out near 
the top of the headings or entrances or the center of the shafts ; 
in summer the air currents will take the contrary direction. 

Natural ventilation in tunnels is improved when the exca- 
vation of the heading reaches a shaft, because the interior air 
can then communicate with the exterior at two points, at dif- 
ferent levels. In such cases a force equal to the difference in 
weight between a column of air in the shaft and a similar one 
of different density at the entrance of the tunnel, will act upon 
the mass of air in the tunnel and keep it in movement, thus 
producing ventilation. Consequently, during winter, when the 
outside air has greater weight than that inside, the air will 
come in by the headings and go out by the shaft, and in the 
summer it will enter at the shaft and pass out at the entrance. 



VENTILATION AND LIGHTING DURING CONSTRUCTION 327 

Sometimes to afford better ventilation shafts 8 or 12 in. in di- 
ameter are sunk exclusively for the purpose of changing the 
air. When the inside temperature is equal to that outside, 
as often happens during the spring and autumn, there are no 
drafts, and consequently the air in the excavation is not re- 
newed and becomes foul ; then fires are lighted under the 
shaft and a draft is artificially produced. The hot air going 
out through the shaft, as through a chimney, allows the fresh 
air to come in as in ordinary ventilation. 

When the head of the excavation is very far from the en- 
trances, or when the mountain is too high to allow excavation 
by shafts, it is quite impossible to secure good natural ventila- 
tion, especially during the spring and autumn months, and the 
engineer has to resort to some artificial means by which to 
supply fresh air to the workmen. 

Artificial Ventilation. — Artificial ventilation in tunnels may 
be obtained in two different ways, known as the vacuum and 
plenum methods. Their characteristic difference consists in 
this, that in the vacuum method the air is drawn from the in- 
side and the vacuum thus produced causes the fresh air from 
the outside to rush in, while the plenum method consists in 
forcing in the fresh air which dilutes the carbonic air produced 
inside the tunnel by workingmen and explosives. In the vac- 
uum method the pressure of the atmosphere inside the tunnel is 
always less than the pressure outside, while in the plenum 
method the pressure within is always greater than that outside. 
Ventilation is the result of this difference of pressure, as the 
tendency of the air toward equilibrium produces continuous 
drafts. Both these methods have their advantages and disad- 
vantages ; but in the presence of hard rock, when explosives are 
continually required, the vacuum method is considered the best, 
because the gases attracted to the exhaust pipes are expelled 
without passing through the whole length of the tunnel, thus 
avoiding the trouble that a draft of foul air will give to the 
workmen who are within the tunnel. In both these methods it 



328 TUNNELING 

is necessary to separate the fresh air from the foul one ; and this 
is done by means of pipes which will exhaust and expel the 
foul air in the vacuum method, or force to the front a current 
of fresh air when the plenum method is used. Artificial venti- 
lation may also be obtained by compressed air which is set free 
after it has driven the machines, especially in tunnels excavated 
through rock, when rock drilling machines moved by com- 
pressed air are employed. 

Vacuum Method Contrivances. — The most common of the vac- 
uum appliances consists in the simple arrangement of a pipe 
leading from the head of the tunnel out through the fire of a 
furnace. The air in the pipe is rarefied by the heat of the fur- 
nace and then set free from the other end of the pipe, thus 
creating a partial vacuum in the pipe, into which the foul air of 
the head rushes, the fresh air from the entrance taking its place, 
and thus ventilating the tunnel. A similar arrangement may 
be used with shafts, and the foul air may be driven out by a 
furnace which is placed either at the top or bottom of the shaft. 
Such furnaces act the same as those commonly used for heating 
purposes in the houses, with this difference, that, instead of fresh 
air being forced in, foul air is expelled. Another simple 
arrangement for producing a vacuum is by means of a steam, 
jet which is thrown into the pipe, and which helps the expul- 
sion of the air by heating it, thus producing a different density 
which originates a draft besides that mechanically originated by 
the force of the steam jet, which tends to carry out the foul air 
of the pipes. 

Foul air may also be expelled by means of exhaust fans 
which are connected with pipes near the entrance of the tunnel. 
The fan consists of a box containing a kind of a paddle wheel 
turned by steam or water power and arranged so as to revolve 
at a high speed. The air inside the pipe is forced out by 
blades attached to the wheel, and thus the foul air of the front 
is driven away and fresh air from the entrance rushes in to take 
its place, and perfect ventilation is obtained. 



VENTILATION AND LIGHTING DURING CONSTRUCTION 329 

The best manner of expelling foul air from tunnels, accord- 
ing to the vacuum method, is by means of bell exhausters. 
This consists of two sets of bells connected by an oscillating 
beam and balancing each other. Each set consists of a movable 
bell, which covers and surrounds a fixed bell with a water joint. 
In the central part of the fixed bell there are valves which open 
upwards, and on the bottom of each movable bell there are 
valves which open from the outside. When one bell ascends, 
the valves at the bottom are closed, the air beneath is then 
rarefied, and a vacuum is produced ; the valves in the central 
part of the fixed bell filled with water are opened, and there is 
an aspiratory action from the pipe leading to the headings, and 
the foul air is thus carried away. The apparatus makes about 
ten oscillations per minute, and the dimensions of the bells 
depend upon the quantity of air to be exhausted in a minute. 
In the St. Gothard tunnel, where these bell exhausters were 
used, they exhausted 16,500 cu. ft. of air per minute. 

Plenum Method Contrivances. — Fresh air may be driven into 
tunnels to dilute the carbonic acid by two different ways, viz., 
by water blast and by fans. Water when running at a great 
velocity produces a movement in the air which may be some- 
times usefully and economically employed for ventilating 
tunnels. Water falling vertically is let run into a large 
horizontal zinc pipe having a funnel at the outer end ; into this 
the air attracted by the velocity of the water is forced. By an 
opening at the bottom the water is afterward withdrawn from 
the pipe, and there remains only the air which is pushed for- 
ward by the air which is being continually sucked in by the 
velocity of the water. 

The best and most common means of ventilation by the 
plenum method is by fans. There are numerous varieties of 
these fans in the market, but they all consist of a kind of fan 
wheel which by rapid revolution forces the fresh air into the 
pipe leading to the headings of the tunnel or to the working 
places. Instead of a large single fan, such as is used for min- 



330 



TUNNELING 



ing purposes, it is better to have a number of small fans acting 
independently of each other, conveying the fresh air where it is 
needed through independent pipes. 

Saccardo's System. — A new method of ventilating tunnels 
was devised by Mr. Saccardo for the ventilation of the Pracchia 
tunnel along the Bologna and Lucca Railway in Italy. At the 
highest end of the tunnel the mouth was contracted inward in a 
funnel shaped form so as to just admit a train. Immediately 
at this contraction, a lateral tunnel, 50 feet long, branched off 
from one side of the main tunnel. At the mouth of this lateral 
tunnel was installed a fan which forced air into the tunnel and 
with 70 revolutions per minute delivered 3.532 cu. ft, of air per 
second at a water pressure of 1 in. This air current was directed 
inward through a second contraction or funnel, parallel to the 
'One at the entrance and 23 ft. beyond it. In operation the 
action of the artificial air current was to suck in a considerable 
volume of outside air, while the air pressure was sufficient to 
counterbalance the movement of air produced by a train mov- 
ing at a velocity of 16.1 ft. per second. Mr. Saccardo ^s method 
was employed in ventilating a tunnel on the Norfolk and West- 
ern Railway with satisfactory results. 

Compressed Air. — In the excavation of tunnels in hard rock 
a number of rock drilling machines are employed which are 
moved by compressed air at a pressure of not less than five 
atmospheres. At each stroke about 100 cu. ins. of compressed 
air are set free, and at an average of 10 strokes per minute there 
would be 5000 cu. ins. of air at five atmospheres or 25,000 
cu. ins., or a little more than 175 cu. ft. of fresh air at normal 
pressure set free every minute by each of the machines employed. 
But the air exhausted from the drilling machine is foul. 

Regarding ventilation by compressed air, Mr. Adolph Sutro, 
in a lecture delivered to the mining students of the University 
of Cahfornia, said: 

"T will note a curious fact which I have never seen explained, and which is 
worthy of close investigation by means of experiments. In the Sutro tunnel 



VENTILATION AND LIGHTING DURING CONSTRUCTION 331 

we found that the compressed air used for driving the machine drills, after 
having been compressed and expanded and discharged from the drills, was not 
wholesome to breathe, and the men and mules would all crowd around the end 
of the blower pipe to get fresh air. Whether the air in being compressed has 
parted with some of its oxygen or because vitiated from some other cause, I do 
not know, and I Kope that this subject will at some future day be carefully 
examined into." 

In the December, 1901, number of ^^ Compressed Air,'^ a 
magazine especially devoted to the useful application of com- 
pressed air, is read : 

Compressed air wasted from power drills is so contaminated with oil from 
the cylinders that it cannot be taken into consideration as ventilation. It is as 
important to displace it with pure air as it is to drive out or draw off other viti- 
ated air. The ventilation should be an independent supply provided by fan 
or blower, delivering by pipe at the point where miners are working. 

Quantity of Air. — The quantity of air to be introduced into 
tunnels must be in proportion to the oxygen consumed by the 
men, the animals, and the explosions. It is allowed that the 
quantity of air required for breathing purpose and explosions is 
as follows: 

1 workman with lamp needs 240 cu. yds. of fresh air in 24 hours. 
1 horse " 850 '' " " 

1 lb. gunpowder 100 " . " " 

1 lb. dynamite 150 " " " 

In a long tunnel excavated through hard rock the number 
of workmen all together may be assumed at 400 at each end, 
and each workman is supposed to be furnished with a lamp. 
No less than ten horses are employed, and the average quantity 
of dynamite consumed is 600 lbs. per day. From the data given 
the consumption of air by workmen and lamps would be: 
240 X 400 = 96,000 cu. yds.; the consumption of air by horses 
would be 850 X 10 = 8500 cu. yds.; the consumption of air by 
dynamite would be 150 X 600 =90,000 cu. yds.; making a 
total consumption of air per day of 194,500 cu. yds., or about 
8000 cu. yds. per hour. 

To obtain good ventilation, then, it will be necessary to 
furnish every hour a quantity of fresh air amounting to not less 



332 TUNNELING 

than 8000 cu. yds. Since, however, a large quantity of pure 
air is expelled with the foul air, it is necessary greatly to in- 
crease this quantity. 

It may be observed, in closing, that the water having its 
particles divided, as in a fog or mist, rapidly precipitates the 
gases produced by explosions. Now, when hydraulic machines 
are used, there is a hollow ball pierced by holes that are almost 
imperceptible, from which the compressed water spreads in very 
subtile particles, and this causes the fall of the gases from 
explosions. Such a method of precipitating gases is very good, 
but does not have the advantage of supplying new oxygen to 
replace that consumed by the men, animals, lamps, and ex- 
plosions; besides, it has the defect of increasing the quantity of 
water to be removed. In tunnels the pipes used either for con- 
veying the fresh air or for carrying away the foul air, are of 
iron, having a diameter of about 8 in.; they are fixed along the 
side walls about 3 ft. above the inverted arch. 

LIGHTING. 

The object and necessity of a perfect lighting of the tunnel- 
workings during construction are so obvious that they need not 
be enlarged upon. Comparatively few tunnels require lighting 
after completion; and these are generally tunnels for passenger 
traffic under city streets, of which the Boston Subway is a rep- 
resentative American example. Considering the methods of 
lighting tunnels during construction, we may, for sake of con- 
venience, chiefly, divide the means of supplying light into (1) 
lamps and lanterns usually burning oil; (2) coal-gas lighting; 
(3) acetylene gas lighting; and (4) electric lighting. 

Lamps and Lanterns. — Lamps and lanterns are commonly 
employed by engineers for making surveys inside the tunnel, and 
to light the instrument. For ranging in the center line, a con- 
venient form of lamp consists of an oil light inclosed in glass 
chimney covered with sheet metal, except for a slit at the front 
and back through which the light shines, and on which the 



VENTILATION AND LIGHTING DURING CONSTRUCTION 333 

observer sights his instrument. To direct the operations of his 
rodmen the engineer usually employs a lantern, either with 
white or colored glass, much like the ordinary railway train- 
man's lantern, which he swings according to some prearranged 
code of signals. 

Lamps and lanterns are used by the workmen both for sig- 
naling and for lighting the workings. For signaling purposes 
red lanterns are usually placed to denote the presence of unex- 
ploded blasts or other points of possible clanger; and colored or 
white lights are usually placed on the front and rear of spoil 
and material trains. For hghting purposes, two forms of lamps 
are employed, which may be somewhat crudely designated as 
lamps for individual use and lamps for general lighting. Indi- 
vidual lamps are usually of small size, and burn oil; they may 
be carried in front of the miner's helmet, or be fixed to stand- 
ards, which can be set up close to the work being done by each 
man. Miners' safety lamps should be employed where there is 
danger from gas. A great variety of lamps for mining and 
tunneling purposes are on the market, for descriptions of 
which the reader is referred to the catalogues of their manu- 
facturers. 

Lamps for general lighting are always of larger size than 
lamps for individual use. A common form consists of a cyl- 
inder ten or twelve inches in diameter, provided with a hook or 
bail for suspension, and filled with benzine, gasolene, or other 
similar oil. Connected with this cylinder is a pipe of con- 
siderable length and small diameter through which the benzine 
or gasolene vapor runs, and burns when lighted with a brilliant 
flame. Lamps of this type burning gasolene were extensively 
employed in building the Croton Aqueduct tunnel. Various 
patented forms of lamps for burning coal-oil products are on 
the market, for descriptions of which the manufacturers' cata- 
logues may be consulted. 

Coal-gas Lig^hting. — A common method of Hghting tunnel 
workings is by piping coal-gas into the headings and drifts from 



334 TUNNELING 

some nearby permanent gas plant, or from a special gas works 
constructed especially for the work. Gas lighting has the great 
advantage over lamps and lanterns of giving a light which is 
more brilliant and steady. Its great objection is the danger of 
explosion caused by leaks in the pipes, by breaks caused by 
flying fragments of rock, and by the carelessness of workmen 
who neglect to turn off completely the burners when they ex- 
tinguish the hghts. In nearly every tunnel where gas has been 
used for hghting, the records of the work show the occurrence 
of accidents which have sometimes been very serious, partic- 
ularly when fire has been communicated to the tunnel tim- 
bering. 

Acetylene Gas Lighting. — The comparatively recent develop- 
ment of acetylene gas manufactured from carbide of calcium 
has given little opportunity for its use in tunnel lighting, and 
the only instance of its use in the United States, so far as the 
author knows, is the water-works tunnel conduit for the city of 
Washington, D. C. Col. A. M. Miller, U. S. Engineer Corps, 
who is in charge of this work, describes the method adopted in 
his annual report for 1899 as follows : — 

"It had been the practice to do all work underground by the light of 
miners' lamps and torches. This means of illumination is very poor for me- 
chanical work. The fumes and smoke from blasting, added to the smoke 
from torches and lamps, render the atmosphere underground, especially when 
the barometer conditions were unfavorable to ventilation, very offensive and 
discomforting to the workmen. An investigation of the subject of lighting 
the tunnel by other means, more especially at the locality where the mechanics 
were at work, — brick and stone masons, and the workmen on the iron lining, 
— resulted in the selection of acetylene gas as the most available and eco- 
nomical in this special emergency. Accordingly, an acetylene gas plant for 
300 burners was erected at Champlain- Avenue shaft, and one for 60 lights at 
Foundry Branch. The engine-houses at the shafts, the head-houses, and local- 
ities in the tunnel, when required, are lighted by these plants. 

''Gas pipes were cariied down the Champlain- Avenue shaft and along the 
tunnel both in an easterly and westerly direction, with cocks for burners at 
proper intervals every 30 feet; and this system sufficed for illumination from 
Rock Creek to Harvard University, a distance of over two miles. The plant 
erected at Foundry Branch was in like manner utilized for the illumination 
from that point in both directions. 

"By connecting with the stopcocks by means of a rubber hose, a movable 



VENTILATION AND LIGHTING DURING CONSTRUCTION 335 

light, chandelier, or 'Christmas-tree' of any required number of burners is 
used, thus concentrating the hght in the immediate vicinity of the work, and 
also enabling the illumination to be carried into the cavities or 'crow-nests,' so 
called, behind the defective old lining. 

"This method of illuminating has proved very satisfactory and quite eco- 
nomical. It is especially valuable as enabling good work to be done, and 
facilitating a thorough inspection of the same." 

Electric Lighting. — By far the most perfect, and at present 
the most commonly employed means for lighting tunnel work- 
ings, is electricity. The light furnished by electric lamps is 
steady and brilliant, and does not consume oxygen or give off 
offensive gases. The wires are easily removed and extended, 
and the lamps are easily put in place and removed. About the 
only objection to the method is the fragility of the lamps, which 
are easily broken by the flying stones and the concussion pro- 
duced by blasting. 



336 TUNNELING 



CHAPTER XXV. 

THE COST OF TUNNEL EXCAVATION AND 
THE TIME REQUIRED FOR THE WORK. 



Cost. — The cost of a tunnel will depend upon the cost of 
the two principal operations required in its construction, viz., 
the excavation of the cross section and the lining of the exca- 
vation with masonry, metal, or timber. These two operations 
may in turn be subdivided, in respect to expense, into cost of 
labor and cost of materials. It is a comparatively simple mat- 
ter to calculate the cost of the building materials required to 
construct a tunnel ; but it is very difficult to estimate with 
accuracy what the cost of labor will be. The reason for this is 
that it is impossible to foresee exactly what the conditions will 
be ; the character of the material may change greatly as the 
work proceeds, increasing or decreasing the cost of excavation ; 
water may be encountered in quantities which will materially 
increase the difficulties of the work, etc. Nevertheless, while 
accurate preliminary estimates of cost are not practicable, it is 
always desirable to attempt to obtain some idea of the probable 
expense of the work before beginning it, and the more usual 
means of getting at this point will be discussed here. 

Two methods of estimating the cost of tunnel work are em- 
ployed. The first is to calculate the probable expense of the 
various items of work, based upon the available data, per unit 
of length, and then add to this a margin of at least 10% to allow 
for contingencies ; the second is to apply to the new work the 
unit cost of some previous tunnel built under substantially the 
same conditions. In the first method it is usual to consider 
the strutting and hauling as constituting a part of the work of 



COST OF EXCAVATION AND TIME KEQUIRED 337 

excavation. To estimate the cost of excavation involves the 
consideration of three general items, viz., the excavation proper, 
the strutting of the walls of the excavation, and the hauling of 
the excavated materials and the materials of construction. 

The cost of excavating the preliminary headings or drifts is 
greater per unit of material removed than that of excavating 
the enlargement of the section. The cost of bottom drifts is 
also always greater than that of top headings, the material pene- 
trated remaining the same. Mr. Rziha gives the comparative 
unit costs of excavating drifts, headings, and enlargement of 
the profile as follows : — 

Bottom drifts $9.20 per cu. yd. 

Top headings 4.80 " " " 

Enlargement of profile 2-84 "" " 

The cost of hauling increases with the length of the tunnel. 
This fact and amount of this increase are indicated by the 
following actual prices for the Arlberg tunnel : — 

Top heading $6.76 per cu. yd., increasing 37 cts. per mile 

Bottom drift 7.40 " " " " 26 " " " 

Enlargement of profile . . . 2.70 " " " " 10 " " " 

In all the prices given above, the cost of strutting and haul- 
ing is included in the cost of excavation. 

The cost of excavation is not always the same for the same 
character of materials in different tunnels. The following 
figures show the prices paid for the excavation of calcareous 
rock in four different German tunnels : — 

Berliner Nordhausen Wetzler R.K f 1.24 per cu. yd. 

Ofen 1.30 " " " 

Staffiach 2.76 " " " 

- Gries 1.92 " " '« 

The method of tunneling has little influence upon the cost 
of the work, as shown by the following figures from tunnels 
excavated through calcareous rock by different methods : — 



338 TUNNELING 

Ofen tunnel Austrian method .|93.19 per lin. ft. 

Dorremberg tunnel Belgian method 86.08 " " " 

Stafflach tunnel English method 91.69 " " " 

The Martha and Merten tunnels, excavated through soft 
ground by the Austrian and Gerroan methods respectively, 
cost 187.95 and $87.55 per hn. ft. respectively. In the exca- 
vation of the various sections of the tunnel for the new Croton 
Aqueduct in America, the following prices were paid : — 

Excavation of heading -f 8 to $10.00 per cu. yd. 

Tunnel in soft ground 8 to 9.00 " " " 

Tunnel in rock 7 to 8.50 " " " 

Brick masonry 10.00 " " " 

Timber in place $40 per M. ft. B. M. 

It is the practice in America to include the work of hauling 
under excavation, but not to include the strutting, which is 
paid for separately. In some cases only the market price of 
the timber is paid for separately, the cost of setting up being 
included in the price of excavation. The writer prefers the 
European practice of including the total cost of timbering 
under excavation, since the two operations are so closely con- 
nected, and since the contractor employs the same timber over 
and over again. Knowing the dimensions of the several mem- 
bers of the strutting, it is a simple, although somewhat tedious, 
process to calculate the total quantity required. An idea of 
the quantity of timber required for stratting in soft ground 
may be had from the data given on page 50. The quantity 
will decrease as the cohesion of the material penetrated in- 
creases, until it becomes so small in hard rock-tunnels as to cut 
very little figure in the total cost. 

The cost of hoisting excavated materials through shafts 
depends upon the depth from which it is hoisted, and upon the 
character of hoisting apparatus employed. The following table, 
showing the cost of hoisting for different lifts and by different 
methods, is given by Rziha, the cost being in francs per cubic 
meter : — 



COST OF EXCAVATION AND TIME REQUIRED 



339 



Height tn 


Windlass. 


HOKSE Gins. 


Steam Hoists. 










Metrks. 


Francs per Cu.M. 


One Horse. 
Francs per Cu. M. 


Two Horses. 
Francs per Cu. M. 


Francs per Cu. M. 


15 


0.172 


0.077 


0.062 


0.035 


30 


0.212 


0.087 


0.070 


0.045 


45 


0.257 


0.100 


0.080 


0.050 


60 


0.305 


0.112 


0.092 


0.082 


90 


0.410 


0.152 


0.110 


0.087 


120 


0.535 


0.195 


0.135 


0.092 


150 


0.722 


0.240 


0.157 


0.112 



Mr. Sejourne, a French engineer, who has been connected 
with the construction of numerous tunnels by the Belgian 
method where he was in position to secure comparative figures, 
has given the following rules for calculating the cost of 
tunnels. Assuming A to represent the cost of excavating a 
cu. yd. in the open air, the cost of excavating the same 
quantity underground in driving headings will be from 9 A to 
11 A, and in enlarging the profile it will be about 5 A. The 
cost of constructing single-track tunnels varies with the thick- 
ness of the lining, and may be calculated by the following 
formulas : 

Without lining, C = 5.5 A. 

With roof arch only, C = 6.4 + 6.4 A. 

With lining 18 in. thick, C = 9.4 + 7 A. 

With lining 2 ft. thick, C = 11 + S A. 

In these formulas C is the cost per cu. yd. of excavation, 
including the masonry. For double-track tunnels the amounts 
given by the above formulas may be used by reducing them 
about 7i % or 8 %. 

The second method of estimating the cost of tunnel work 
consists in assuming as a unit the unit cost of tunnels pre- 
viously excavated under similar conditions. Mr. La Dame 
gives the following unit prices for a number of tunnels driven 
through different materials ; 



340 



TUNNELING 



Nature of Soil. 




EXCAV. PER 

Cu. Yd, 


Cost per 
Lin. Ft. 


Max. and Min. 
per Lin. Ft. 


Granite-gneiss . . 

Schist 

Triassic 

Jm-assic .... 
Cretaceous .... 
Tertiary and modern 


56 
39 
3 
69 
34 
39 


$3.07 @$3.85 
1.38 @ 1.53 

1.23 @" l!38 
0.61 @ 0.77 
0.33 @ 0.61 


$100. 
75.42 

90.85 

77.86 

59.60 

105.80 


$61.46 @ $190.40 
43.11 @ 70.68 
84.75 @ 93.33 
35.24 @ 157.2 
27.37 @ 92.25 
51.52 @ 188.36 



In the following table is given a list of tunnels excavated 
through different soils, from the most compact to very loose 

DOUBLE-TRACK TUNNELS. 



Name of Tunnels, 


Quality of Soil. 


Cost per 
Lin. Ft. 


Method of 
Tunneling. 


Mt. Cenis 

St. Gothard 

Stammerich 

italic . 

Bothenfels 

Dorremberg .... 

Stafflach 

Ofen 

Wartha 

Mertin 

Scloss Matrei .... 
Trietbitte 


Granitic, 

Granitic, 

Broken schist, 
Dolomite, 
Calcareous, 
Calcareous, 
Calcareous, 
Grewack, 
Grewack, 
Clay schist, 

Clay and sand. 


$273.73 

] 93.63 

157.90 

290.58 

115.64 

86.08 

91.69 

93.19 

87.95 

87.55 

94.25 

229.0 

69.50 

178.0 

182.31 


Drift. 

Heading. 

English. 

Austrian. 

English. 

Belgian. 

English. 

Austrian. 

Austrian. 

German. 

English. 

German. 

Wide heading. 


Canaan 

Church-Hill .... 
Bergen No. 1 . . . . 


Clay-slate, 
Clay with shells, 
Trap rock. 



SINGLE-TRACK TUNNELS. 



Name of Tunnels. 


Quality of Soil. 


Cost per 
Lin. Ft. 


Method of 
Tunneling. 


Mt. Cenis 

Stalletti 

Marein 

Welsberg 

Sancina 

Starre 

Cristina 

Burk 

Brafford Ridge . . . . 

Dunbeithe 

Fergusson 

Port Henry 

Points 


Gneiss, 
Granite and quartz, 

Clay schist. 

Gravel, 
Clay of 1st variety, 
Clay of 2d variety. 
Clay of 3d variety, 

Limestone, 
Sandstone, 
Limestone, 
Granite, 


$82.27 

62.75 

64.36 

165.07 

129.40 

191.61 

307.42 

83.90 

85.33 

70.47 

37.46* 

so.oot 

72.00* 


Heading. 

Austrian. 

English. 

Austrian. 

Belgian. 

Belgian. 

Italian. 
Wide heading. 
Wide heading. 
Wide heading. 
Wide heading. 
Wide heading. 
Wide heading. 



* Are unlined. 



t Lined with timber. 



COST OF EXCAVATION AND TIME REQUIRED 341 

materials, and driven according to the various methods v^hich 
have been illustrated. 

The Habas tunnel through quicksand, between Dax and 
Ramoux, France, cost 1118.50 per lin. ft. The cost of 
the Boston subway was 1342.40 per lin. ft. The Severn 
and Mersey tunnels, constructed through rock under water, 
cost respectively 1208.33 and |263 per lin. ft. The First 
Thames Tunnel, driven by Brunei's shield, cost $1661.66 per 
lin. ft. The Hudson River and St. Clair River tunnels, exca- 
vated through soft ground by means of shields and compressed 
air, cost respectively 1305 and |315 per lin. ft. The Black- 
wall double-track tunnel under the River Thames, which is 
the largest tunnel ever built by the shield system, cost $600 
per lin. ft. 

In making estimates of the cost of projected tunnel work 
based on the cost of tunnels previously constructed through 
similar materials, it is important to keep in mind the date and 
location of the work used as the basis for calculations. For 
example, a tunnel excavated in Italy, where labor is very cheap^ 
will cost less than one excavated in America, where labor is 
dear, all other conditions being the same. Other reasons for 
variation in cost due to difference of date and location of con- 
struction will suggest themselves, and should be taken into full 
consideration in estimating the cost of the new work. 

Time. — The time required to excavate a tunnel depends 
upon the character of the material penetrated and upon the 
method of work adopted. Tunnels driven through soft ground 
by hand require about the same time to construct as tunnels 
driven through hard rock by the aid of machinery. Tunnels 
can be driven through hard rock at about as great a speed as 
through soft or fissured rock, chiefly because the work of 
blasting is more efficient in hard rock, and because no time 
is required in timbering. The following table shows the 
average rate of progress in different parts of the tunnel excava- 
tion through both hard and soft materials in feet per month : — 



342 



TUNNELING 



Quality of Soil. 


Headikg. 


Excavation of Shafts. 


Enlarge- 
ment OF 
Profile. 


By hand. 


By macliine. 


By hand. 


By machine. 


By hand. 


Very loose soil . 
Loose soil . . 
Soft rock . . . 
Hard rock . . 
Very hard rock. 


16.7 -26.8 

33.4 -100 

66.8 

50 -66.8 

33.4 


233.8-334 
233.8-334 
233.8-334 


6.6-16.7 
16.7-33.4 
33.4-66.8 
33.4-50 
16.7-33.4 


66.8-132.6 
66.8-132.6 
66.8-132.6 


6.6-16.7 
16.7-33.4 
33.4-50 
66.8-100 
66.8-100 



The following tables showing the average rate of progress 
have been compiled from the actual records made in the 
tunnels named : 



Name of Tunnel. 


DlxMENSIONS 

IN Feet. 


pi 


Character of 
Material. 


Observations. 


Excavation of headings 










by hand: 










Mount Cenis . . 


10X10 


65.8 


Schist, 


Bottom drift. 


Sutro 


6.7 X5.7 


70.14 


Quartzose, 




St. Gothard . . . 


8.4x8.7 


70.14 


Granite, 


Top heading. 


Excavation of headings 










by machine: 










Mount Cenis 


10 X 10 


188.7 


Calcareous schist, 


Bottom drift. 


Sutro .... 


8.15X10 


227.45 


Quartzose, 




St. Gothard 




8.4X8.7 


339.45 


Granite, 


Top heading. 


Trari . . 




8 X 9.35 


167 


Gneiss, 


Top heading. 


Arlberg . 




8.35 X 9.35 


474.2 


Mica schist, 


Bottom drift. 


Palisades . 




16x7 


160 


Trap rock. 


Top heading. 


Busk . . 




15x7 


126 


Granite, 


Top heading. 


Cascade . 




16 X 8 


180 


Basaltic rock. 


Top heading. 


Franklin . 




15 X 7 


240 





Top heading. 



The following table shows the monthly progress of com- 
pleted tunnel in feet excavated through rock : 



Name of Tunnel. 


Progress 
IN Feet. 


Material. 


Method. 


Cascade 

Palisades 

Busk 

Tennessee Pass 


207 
186 
190 
169.5 


Basalt, 
Trap rock, 
Granite, 
Granite, 


Top heading. 
Top heading. 
Top heading. 
Top heading. 



COST OF EXCAVATION AND TIME REQUIRED 



343 



The average monthly progress in feet of excavating tunnels 
through treacherous ground may be quite generally assumed 
to be for: (1) clay of the first variety from 43.4 ft. to 60 ft. ; 
for clay of the second variety from 33.4 ft. to 43.4 ft. ; for clay 
of the third variety from 23.3 ft. to 33.4 ft., and for quicksand 
from 30 ft. to 50 ft. The monthly progress in feet made in 
sinking the shafts of the Hoosac and Musconetcong tunnels in 
America was as follows : — 



Name of Tunnkl. 


DiMENSIOKS 

IN Feet. 


Depth 
IN Feet. 


Pbogkess 
IN Feet. 


Character 
OF Material. 


Hoosac: 

East shaft 

West shaft 

Musconetcong: 

Vertical shaft .... 


15.4X27.7 
8X16 

8.35 X 16.7 


1035 
267 

113.5 
304. 


21.7 
16.7 

100 
32 


Mica schist. 
Gneiss. 

Loose rock. 
Loose rock. 


Inclined, shaft .... 


8 35 X 26 







The average monthly progress of sinking shafts in treach- 
erous soils may be assumed to be as follows : clay of first 
variety, 50 ft. to 75 ft. ; clay of second variety, 36.75 to 50 ft; 
clay of third variety, 23.4 ft. to 36.75 ft. ; quicksand, 16.7 ft. 
to 33.4 ft. 

For the reason that the details change with the various 
conditions encountered in every work, all the tunnel operations 
have been treated in a general way, purposely avoiding to give 
any detail. Also the rate of progress and items of cost of tun- 
nels have been given in a broad manner because they greatly 
vary in the different works. This information, however, can 
be easily obtained by consulting the Engineering Magazines, 
where are reported all the tunnel works of America and Europe, 
and where are given so many details which are very valuable 
to expert engineers in charge of similar works, but not to stu- 
dents and people who are looking only for general knowledge. 



INDEX 



Accidents and Repairs in the Belgian 

Method, 152 
Accidents in Tunnels: 

After Construction, 308 

Baltimore Belt Line, 165 

Chattanooga Tunnel, 311 

During Construction, 301 

General Discussion, 301 

Giovi Tunnel, 309 

Repairing of, 304 
Acetylene Gas Lighting, 334 
Air Compressors, Description of, 87 
Air Locks, 264-272 
Air Pressure, 268 
American Method : 

General Description, 172 

Excavation, 172 

Strutting, 174 

Hauling, 175 
Arrangement of Drill Holes, 90 
Artificial Ventilation, 327 
Austrian Method of Tunneling: 

Advantages and Disadvantages, 
180 

Excavation, 176 

General Description, 176 

Lining, 180 

Strutting, 177 
Average Progress in Tunnels, 342 

Baltimore Belt Line Tunnel, General 

Description, 160 
Barlow's Shield, 242 
Beach's Shield, 246 
Belgian Method: 

Accidents and Repairs, 152 

Advantages and Disadvantages, 
152 

Excavation, 145 

General Description, 144 

Lining, 148 

Hauling, 150 

Strutting, 146 
Bench, 131 
Bends, 268 
Blackwall's Tunnel Shield, 248 



Blasting-cone, 33 
Bhckford Match, 31 
Boston Subway: 

General Descriptions, 203 

Roof Shield, 251 
Boulder Tunnel Relined, 315 
Box-cars, 61 
Box Strutting, 51 
Brandt DrilHng Machine, 28, 112 
Brown, W. L., 269 
Brunei's Shield, 240 

Caissons, 293 

Canals and Pipe Lines, 86 

Cascade Tunnel, 98 

Center-cut, 91 

Center Line: 

Curvilinear Tunnels, 14 

Determination of, 9 

Rectihnear Tunnels, 9 

Simplon Tunnel, 106 

Submarine Tunnels, 265 

Triangulation, 12 

Transferred through Center Shafts, 
13 

Transferred through Side Shafts, 
14 

Value's Device, 10 
Centers : 

For Arches, 68 

EngHsh Method, 169 

Ground Molds, 66 

Itahan Method, 184 

Lagging, 71 

Leading Frames, 67 

Setting Up, 70 

Striking, 71 
Chattanooga Tunnel, Accident, 311 
City and South London Railway 

Shield, 250 
Classification of Tunnels, 42 
Coal-gas Lighting, 333 
Cofferdam Method of Tunneling, 281 

Van Buren Street Tunnel, Chicago, 
282 
Collapse of Tunnels, 302 



345 



346 



INDEX 



Compressed Air: 

For Power, 87 

For Ventilation, 330 
Concrete Lining, 75 

Fort George Tunnel, 139 

Murray Hill Tunnel, 126 
Cost of: 

Double-track Tunnels, 340 

Hauling, 338 

Headings, 337 

Hoisting, 338 

Single-track Tunnel, 340 

Submarine Tunnels, 341 

Subways, 209-217 

Tunnels, 336 
Craven, Alfred, 39 
Craven's Sunflower, 39 
Cross-section : 

Dimensions of, 20 

Form of, 18 

Hudson River Tunnel Pennsyl- 
vania Railroad, 277 
Crown-bar (see American Method). 

Subways, 204-211 
Croton Aqueduct Tunnel, 95 
Culverts, 80 

Detroit River Tunnel, 296 
Diamond Drilling Machine, 27 
Directing the Shield, 265 
Drift, 37 
Drift Method: 

General Discussion, 102 

Murray Hill Tunnel, 123 

Simplon Tunnel, 103 
DriJhng Machines: 

Brandt, 112 

Ingersoll, 26 
Drills: 

Diamond, 27 

Hand, 23 

Mountings for, 25 

Percussion, 24 

Power, 24 

Rotary, 27 
Dumping Cars, 60 

Electric Firing, 32 
Electric Lighting, 335 
EngHsh Method: 

Advantages and Disadvantages, 
171 

Centers, 169 

Excavation, 166 

General Discussion, 166 

Lining, 170 

Strutting, 167 



Enlargement of the Profile, 38 
Entrances, 81 
Erector, 272 
Excavation : 

American Method, 172 

Arrangement of Drill Holes, 90 

Austrian Method, 176 

Belgian Method, 145 

Center-cut, 91 

Enlargement of Profile, 38 

English Method, 166 

Fort George Tunnel, 136 

German Method, 155 

Headings, 37, 91 

Hudson River Tunnel of Pennsyl- 
vania Railroad, 273 

Itahan Method, 182 

Murray Hill Tunnel, 124 

Quicksand Method. 189 

Pilot Method, 193 

Shield and Compressed Air 
Method, 267 

Simplon Tunnel, 110 
Excavating Machines: 

For Earth, 22 

For Rock, 23 
Explosions, 33 

Dynamite, 30 

Gunpowder, 28 

Nitroglycerine, 29 

Quantity of, 34 

Storage of, 30 

Failure of Tunnel Roof, 305 
Forgie, James, 269 
Fort George Tunnel, 135 
Foundations for Lining, 76 
Fox, Charles B., 103 
Frame Strutting, 49 
Fuses, 31 

Geological Survey, 3 
German Method: 

Advantages and Disadvantages, 159 

Excavation, 155 

General Description, 155 

HauHng, 158 

Strutting, 156 
Giovi Tunnel Accident, 309 
Graveholz Tunnel, 98 
Greathead's Shield, 245 

Hand Drills, 23 
Harlem River Tunnel, 285 
HauUng: 
American Method, 175 



INDEX 



347 



Hauling: Continued 

Belgian Method, 150 

Italian Method, 185 

German Method, 158 

Hudson River Tunnel of Penn- 
sylvania Raihoad, 278 

Motive Power, 61 

By Way of Entrances, 59 

Simplon Tunnel, 111 

By Way of Shafts, 62 
Heading and Bench Method: 

Fort George Tunnel, 135 

General Discussion, 130 

St. Gothard Tunnel, 1 
Headings, 37, 91 
Hewett, H. B., 269 
History of Tunnels, xiii 
Hoisting Machines: 

General Discussion, 62 

Elevators, 64 

Horse Gins, 63 

Windlass, 63 
Hoosac Tunnel, 93 
Hopkins, Stephen W., 135 
Hudson River Tunnel of Pennsyl- 
vania Railroad, 269 
HydrauHc Jacks, 260, 271 
Hydraulic Rams, 271 



Illumination : 

Acetylene Gas, 334 

Coal-gas, 333 

Electric, 335 

Hudson River Tunnel of Pennsyl- 
vania Railroad, 280 

Lamps and Lanterns, 330 
Inclination of Strata, 6 
IngersoU Drilling Machine, 26 
Inverted Arch Lining, 77 
Iron and Masonry Lining, 74 
Iron Lining, 73, 261, 276 
Iron Strutting, 55 

Full Section, 56 

Headings, 56 

Shafts, 57 
Itahan Method: 

Advantages and Disadvantages, 
188 

Excavation, 182 

General Description, 182 

Modifications, 186 

Strutting, 183 



Jacks, 260, 271 

Joining the Caissons, 295 



Lagging, 71 

Lamps and Lanterns, 330 

Lighting (see Illumination). 

Lining: 

Austrian Method, 180 

Belgian Method, 148 

Concrete, 126, 139 

Enghsh Method, 170 

Foundations, 76 

General Observations, 78 

German Method, 158 

Hudson River Tunnel Pennsyl- 
vania Railroad, 276 

Invert, 77 

Iron, 73, 261, 276 

Iron and Masonry, 74 

Itahan Method, 185 

Masonry, 74 

Quicksand Method, 191 

Roof Arch, 77 

Side Tunnels, 79, 83 

Side WaUs, 77 

Subways, 207-213 

Timber, 72 

Thickness of Masonry, 78, 83 
Little Tom Tunnel Relined, 321 
Loose Soil (see Soft Ground). 

Masonry (see Centers) . 

Masonry Culverts, 80 

Masonry (see Lining). 

Masonry Lining, 74 

Masonry Niches, 81 

McBean, Daniel, 285 

Mechanical Installations for Tunnel 

Work, 84 
Milwaukee Tunnel, 226 
Mont Cenis Tunnel, 92 
Monthly Progress of Tunnels, 342 
Mullan Tunnel ReUned 319 
Murray HiU Tunnel, 123 

Natural Ventilation, 326 

New York Rapid Transit Subway, 

209 
Niagara Falls Power Tunnel, 97 

Niches, 81 

Open Cut or Tunnel, 1 

Open-cut Tunneling: 
General Discussion, 195 
Parallel Longitudinal Trenches, 197 
Single Trench, 196 
Single Narrow Trench, 197 
Transverse Trenches, 200 
Tunnels on the Surface, 200 



348 



INDEX 



Palisade Tunnel, 94 

Pennsylvania Railroad Shield, 270 

Percussion Drills, 24 

PUot Method of Tunneling, 192 

Plank Centers, 69 

Platform Cars, 59 

Plenum Method of Ventilation, 329 

Pneumatic Caissons, 287 

Polar Protractor, 39 

Portals, 81 

Power Drills, 24 

Power Plants: 

Air Compressors, 87 

Canals and Pipe Lines, 86 

Cascade Tunnel. 98 

Croton Aqueduct Tunnel, 95 

General Description, 84 

Graveholz Tunnel, 98 

Hoosac Tunnel, 93 

Hudson River Tunnel Pennsyl- 
vania Railroad, 279 

Mont Cenis Tunnel, 92 

Murray Hill Tunnel, 128 

Niagara Falls Power Tunnel, 97 

PaHsades Tunnel, 94 

Receivers, 89 

Reservoirs, 86 

Simplon Tunnel, 117 

Sounstein Tunnel, 99 

St. Clair River Tunnel, 99 

St. Gothard Tunnel, 133 

Steam, 85 

Strickler Tunnel, 96 

Turbines, 86 
PreUni's Shield, 251 
Presence of Water, 7 
Prevention of Collapse, 303 
Progress in Sinking Shafts, 343 
Progress of Excavation, 342 
Progress of the Work, 342 
Progress in Simplon Tunnel, 122 

Quantity of Air for Ventilation, 331 
Quicksand Tunneling: 

General Discussion, 188 

Removing the Seepage Water, 191 
Quantity of Timber in Strutting, 54 

Receivers, 89 
Rehning Tunnels, 315 

Boulder Tunnel, 315 

Little Tom Tunnel, 321 

MuUan Tunnel, 319 
Repairing of Accidents in Tunnels, 308 
Reservoirs, 86 
Roof Arch Lining, 77 
Roof Shield for Boston Subway, 251 



Roof of Caissons, 287-291 
Rotary Drills, 27 
Ryder, B. H. 

Saccardo System of Ventilation, 330 

Saunders, W. L., 88 

Seepage Water, 191 

Seine River Tunnel, 293 

Setting up Centers, 70 

Severn Tunnel, 221 

Shafts, Description of, 40 

Shaler, Ira A, 142 

Shield and Compressed Air Method, 

263 
Shield Construction: 

Diaphragm, 256 

Cellular Division, 255 

Dimensions of Shields, 259 

Front End, 254 

General Form, 252 

Rear End, 257 

SheU, 253 
Shield Method: 

Barlow Shield, 242 

Beach's Shield, 245 

Blackwall Tunnel Shield, 248 

Brunei Shield, 240 

City and South London Railway 
Shield, 250 

Greathead's Shield, 245 

History, 238 

Prelini's Shield, 251 

St. Clair River Tunnel Shield, 247 
Side Shafts, 41 
Side Tunnels Lining, 79 
Side WaUs Lining, 77 
Simplon Tunnel, 103 
Soils Encountered in Tunnels, 3 
Sounstein Tunnel, 99 
Stations of Subways, 207-216 
St. Clair River Tunnel Shield, 247 
St. Gothard Tunnel, 132 
Steam Power Plant, 85 
Stratification of the Soils, 6 
Strickler Tunnel, 96 
Striking the Centers, 71 
Strutting: 

American Method, 174 

Austrian Method, 177 

Belgian Method, 146 

Dimensions of Timber, 54 

Pnghsh Method, 167 

Fort George Tunnel, 137 

Full Section, 51 

German Method, 156 

Headings, 48 

Italian Method, 183 



INDEX 



349 



Strutting: Continued 

Murray HiU Tunnel, 125 

Pilot Method, 193 

Quantity of Timber, 54 

Shafts, 52 

Iron: Full Section, 56 
Headings, 56 
Shafts, 57 
Submarine Tunneling: 

Cofferdam Method, 281 

Compressed Air Method, 225 

Detroit River Tunnel, 296 

General Discussion, 218 

Harlem River Tunnel, 285 

Hudson River Tunnel Pennsyl- 
vania Railroad, 269 

Lining, 261 

Milwaukee Water-Works Tunnel, 
226 

Pneumatic Caisson Method, 284 

Seine River Tunnel, 293 

Severn Tunnel, 221 

Shield and Compressed Air Method, 
263 

Shield System, 238 

Sinking and Joining Sections Built 
on Land, 293 

Van Buren Street Tunnel, 282 
Subways : 

Boston, 203 

Cost of, 209-217 

Cross-sections, 204-211 

General Discussion, 195-202 

Lining, 207-213 

New York Rapid Transit Railway, 
209 

Stations, 207-216 
Sutro, Adolph, 330 

Tamping, 32 

Thickness of Lining Masonry, 78, 83 

Thomson Excavating Machine, 22 

Timber Lining, 72 

Timbering (see Strutting). 

Tremies, 299 

Trussed Centers, 70 

Tunnel or Open Cut, 1 

Tunnels : 

Baltimore Belt Line, 160 

Classification of, 42 



Tunnels: Continued 
Fort George, 135 
Murray HiU, 123 
Simplon, 103 
St. Gothard, 132 
Hard Rock, 84 

Drift Method, 102 

Comparison of Methods, 141 

Heading and Bench Method, 152 

Heading Method, 130 
Soft Ground: 

American Method, 172 

Austrian Method, 176 

Belgian Method, 144 

Enghsh Method, 166 

German Method, 155 

Itahan Method, 182 

Pilot Method, 192 

Quicksand Method, 188 
Submarine : 

Detroit River Tunnel, 296 

Harlem River Tunnel, 285 

Hudson River Tunnel of Penn- 
sylvania Railroad, 269 

Milwaukee Tunnel, 226 

Seine River Tunnel, 293 

Severn Tunnel, 221 

Van Buren Street Tunnel, Chi- 
cago, 282 
Under City Streets: 

General Description, 201 

Boston Subway, 203 
Turbines, 86 

Vacuum Method of Ventilation, 328 
Value, Beverley R. 10 
Van Buren Street Tunnel, 282 
Ventilation, 325 

Artificial, 327 

Compressed Air, 330 

Natural, 326 

Plenum Method, 329 

Quantity of Air, 331 

Saccardo's System, 330 

Simplon Tunnel, 120 

Vacuum Method, 328 
Vernon-Har court, L. F., 221 

Working Platforms, 286 
Wyman, Erastus, 293 



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Bottcher, A. Cranes: Their Construction, Mechanical Equipment and 

Working. Trans, by A. Tolhausen 4to, *io 00 

Bottler, M. Modern Bleaching Agents. Trans, by C. Salter i2mo, *2 50 

Bottone, S. R. Magnetos for Automobilists i2mo, *i 00 

Boulton, S. B. Preservation of Timber, (Science Series No. 82.) . i6mo, o 50 

Bourgougnon, A. Physical Problems. (Science Series No. ii3.)..i6mo, o 50 
Bourry, E. Treatise on Ceramic Industries. Trans, by J. J. Sudborough. 

8vo, *5 00 

Bow, R. H. A Treatise on Bracing 8vo, i 50 

Bowie, A. J., Jr. A Practical Treatise on Hydraulic Mining 8vo, 5 00 

Bowker, W. R. Dynamo, Motor and Switchboard Circuits 8vo, *2 50 

Bowles, 0. Tables of Common Rocks. (Science Series No. 125.). . i6mo, o 50 

Bowser, E. A. Elementary Treatise on Analytic Geometry i2mo, i 75 

Elementary Treatise on the Differential and Integral Calculus. 12 mo, 2 25 

Elementary Treatise on Analytic Mechanics i2mo, 3 00 

Elementary Treatise on Hydro-mechanics i2mo, 2 50 

A Treatise on Roofs and Bridges i2mo, *2 25 

Boycott, G. W. M. Compressed Air Work and Diving.. 8vo, *4 00 

Bragg, E. M. Marine Engine Design. i2mo, *2 00 

Brainard, F. R. The Sextant. (Science Series No. loi.) i6mo, 

Brassey's Naval Annual for 191 1 8vo, *6 00 

Brew, W. Three-Phase Transmission 8vo, *2 00 

Brewer, R. W. A. The Motor Car i2mo, *2 00 

Briggs, R., and Wolff, A. R. Steam-Heating. (Science Series No. 

67.) i6mo, o 50 

Bright, C. The Life Story of Su- Charles Tilson Bright. 8vo, *4 50 

British Standard Sections 8x15 *i 00 

Complete list of this series (45 parts) sent on application. 
Broadfoot, S. K. Motors, Secondary Batteries. (Installation Manuals 

Series) i2mo, *o 75 

Broughton, H. H. Electric Cranes and Hoists *9 00 

Brown, G. Healthy Foundations. (Science Series No. 80.) i6mo, o 50 

Brown, H. Irrigation 8vo, *5 00 

Brown, Wm. N. The Art of Enamelling on Metal i2mo, *i 00 

Handbook on Japanning and Enamelling i2mo, *i 50 

• House Decorating and Painting i2mo, *i 50 

History of Decorative Art i2mo, *i 25 

Dipping, Burnishing, Lacquering and Bronzing Brass Ware. . . i2mo, *i 00 

Workshop Wrinkles 8vo, *i 00 

Browne, R. E. Water Meters. (Science Series No. 81.) i6mo, o 50 

Bruce, E. M. Pure Food Tests i2mo, *i 25 

Bruhns, Dr. New Manual of Logarithms 8vo, half morocco, 2 50 

Brunner, R. Manufacture of Lubricants, Shoe Polishes and Leather 

Dressings. Trans, by C. Salter 8vo, *3 00 

Buel, R. H. Safety Valves. (Science Series No. 21.) i6mo, o 50 

Bulman, H. F., and Redmayne, R. S. A. Colliery Working and Manage- 
ment 8vo, 6 00 

Burgh, N. P. Modern Marine Engineering 4to, half morocco, 10 00 



6 D. VAN NOSTRAND COMPANY'S SHORT TITLE CATALOG 

Burt, "W. A. Key to the Solar Compass i6nio, leather, 2 50 

Burton, F. G. Engineering Estimates and Cost Accounts i2mo, *i 50 

Buskett, E. W. Fire Assaying i2mo, *i 25 

Cain, W. Brief Course in the Calculus i2mo, *i 75 

Elastic Arches. (Science Series No. 48.) i6mo, o 50 

Maximum Stresses. (Science Series No. 38.) i6mo, o 50 

Practical Designing Retaining of Walls. (Science Series No. 3.) 

i6mo, o 50 
Theory of Steel-concrete Arches and of Vaulted Structures. 

(Science Series No. 42.) i6mo, o 50 

Theory of Voussoir Arches. (Science Series No. 12.) i6mo, o 50 

Symbolic Algebra. (Science Series No. 73.) i6mo, o 50 

Campin, F. The Construction of Iron Roofs 8vo, 2 00 

Carpenter, F. D. Geographical Surveying. (Science Series No. 37.) . i6mo. 

Carpenter, R. C, and Diederichs, H. Internal Combustion Engines. 8vo, *$ 00 

Carter, E. T. Motive Power and Gearing for Electrical Machinery . . 8vo, *5 00 

Carter, H. A. Ramie (Rhea), China Grass i2mo, *2 00 

Carter, H. R. Modern Flax, Hemp, and Jute Spinning 8vo, *3 00 

Cathcart, W. L. Machine Design. Part I. Fastenings 8vo, *3 00 

Cathcart, W. L., and Chaffee, J. I. Elements of Graphic Statics 8vo, *3 00 

Short Course in Graphics i2mo, i 50 

Caven, R. M., and Lander, G. D. Systematic Inorganic Chemistry. i2mo, *2 00 

Chambers' Mathematical Tables 8vo, i 75 

Charnock, G. F. Workshop Practice. (Westminster Series.). . . .8vo {In Press.) 

Charpentier, P. Timber 8vo, *6 00 

Chatley, H. Principles and Designs of Aeroplanes. (Science Series.) 

No. 126.) i6mo, o 50 

How to Use Water Power i2mo, *i 00 

Child, C. T. The How and Why of Electricity i2mo, i 00 

Christie, W. W. Boiler- waters. Scale, Corrosion, Foaming 8vo, *3 00 

Chimney Design and Theory 8vo, *3 00 

Furnace Draft. (Science Series No. 123.) i6mo, o 50 

Church's Laboratory Guide. Rewritten by Edward Kinch 8vo, *2 50 

Clapperton, G. Practical Papermaking 8vo, 2 50 

Clark, A. G. Motor Car Engineering. Vol. 1. Construction *3 00 

Clark, C. H. Marine Gas Engines i2mo, *i 50 

Clark, D. K. Rules, Tables and Data for Mechanical Engineers 8vo, 5 00 

Fuel: Its Combustion and Economy i2mo, i 50 

The Mechanical Engineer's Pocketbook i6mo, 2 00 

Tramways: Their Construction and Working 8vo, 7 50 

Clark, J. M. New System of Laying Out Railway Turnouts i2mo, i 00 

Clausen-Thue, W. ABC Telegraphic Code. Fourth Edition i2mo, *5 00 

Fifth Edition 8vo, *7 00 

The A I Telegraphic Code 8vo, *7 50 

Cleemann, T. M. The Railroad Engineer's Practice 12 mo, *i 50 

Clerk, D., and Idell, F. E. Theory of the Gas Engine. (Science Series 

No. 62.) i6mo, o 50 

Clevenger, S. R. Treatise on the Method of Government Surveying. 

i6mo, morocco 2 50 

Clouth, F. Rubber, Gutta-Percha, and Balata 8vo, *5 00 



D VAN NOSTRAND COMPANY'S SHORT TITLE CATALOG 7 

Coffin, J. H. C. Navigation and Nautical Astronomy i2mo, *3 50 

Colburn, Z., and Thurston, R. H. Steam Boiler Explosions. (Science 

Series No. 2.) i6mo, o 50 

Cole, R. S. Treatise on Photographic Optics i2mo, i 50 

Coles-Finch, W. Water, Its Origin and Use 8vo, *5 00 

Collins, J. E. Useful Alloys and Memoranda for Goldsmiths, Jewelers. 

i6mo o 50 

Constantine, E. Marine Engineers, Their Qualifications and Duties. 

8vo, *2 00 

Coombs, H. A. Gear Teeth. (Science Series No. 120.) i6mo, o 50 

Cooper, W. R. Primary Batteries 8vo, *4 00 

" The Electrician " Primers . . . • Svo, *5 00 

Part I *i 50 

Part II *2 50 

Part III *2 00 

Copperthwaite, W. C. Tunnel Shields 4to, *9 00 

Corey, H. T. Water Supply Engineering Svo (In Press.) 

Corfield, W. H. Dwelling Houses. (Science Series No. 50.) i6mo, o 50 

Water and Water-Supply. (Science Series No. 17.) i6mo, o 50 

Cornwall, H. B. Manual of Blow-pipe Analysis Svo, *2 50 

Courtney, C. F. Masonry Dams Svo, 3 50 

Cowell, W. B. Pure Air, Ozone, and Water i2mo, *2 00 

Craig, T. Motion of a Solid in a Fuel. (Science Series No. 49.) .... i6mo, o 50 

Wave and Vortex Motion. (Science Series No. 43.) i6mo, o 50 

Cramp, W. Continuous Current Machine Design Svo, *2 50 

Crocker, F. B. Electric Lighting. Two Volumes. Svo. 

Vol. I. The Generating Plant 3 00 

Vol. II. Distributing Systems and Lamps 3 00 

Crocker, F. B., and Arendt, M. Electric Motors Svo, *2 50 

Crocker, F. B., and Wheeler, S. S. The Management of Electrical Ma- 
chinery i2mo, *i 00 

Cross, C. F., Be van, E. J., and Sindall, R. W. Wood Pulp and Its Applica- 
tions. (Westminster Series.) Svo, *2 00 

Crosskey, L. R. Elementary Perspective Svo, i 00 

Crosskey, L. R., and Thaw, J. Advanced Perspective Svo, i 50 

Culley, J. L. Theory of Arches. (Science Series No. S7.) i6mo, o 50 

Davenport, C. The Book. (Westminster Series.). Svo, *2 00 

Davies, D. C. Metalliferous Minerals and Mining Svo, 5 00 

Earthy Minerals and Mining Svo, 5 00 

Davies, E. H. Machinery for Metalliferous Mines Svo, S 00 

Davies, F. H. Electric Power and Traction Svo, *2 00 

Dawson, P. Electric Traction on Railways Svo, *9 00 

Day, C. The Indicator and Its Diagrams i2mo, *2 00 

Deerr, N. Sugar and the Sugar Cane Svo, *8 00 

Deite, C. Manual of Soapmaking. Trans, by S. T. King 4to, *5 00 

De la Coux, H. The Industrial Uses of Water. Trans, by A. Morris . Svo, *4 50 

Del Mar, W. A. Electric Power Conductors Svo, *2 00 

Denny, G. A. Deep-level Mines of the Rand 4to, *io 00 

Diamond Drilling for Gold *5 00 

De Roos, J. D. C. Linkages. (Science Series No. 47.) i6mo, o 50 



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8 D. VAN NOSTRAND COMPANY'S SHORT TITLE CATALOG 

Derr, W. L. Block Signal Operation Oblong i2mo, 

Desaint, A. Three Hundred Shades and How to Mix Them 8vo, 

De Varona, A. Sewer Gases. (Science Series No. 55.) i6nio, 

Devey, R. G. Mill and Factory Wiring. (Installation Manuals Series.) 

i2nio, 

Dibdin, W. J. Public Lighting by Gas and Electricity 8vo, 

Purification of Sewage and Water Svo, 

Dichmann, Carl. Basic Open-Hearth Steel Process i2mo, 

Dieterich, K. Analysis of Resins, Balsams, and Gum Resins Svo, 

Dinger, Lieut. H. C. Care and Operation of Naval Machinery i2mo, 

Dixon, D. B. Machinist's and Steam Engineer's Practical Calculator. 

i6mo, morocco, i 25 
Doble, W. A. Power Plant Construction on the Pacific Coast {In Press.) 
Dodd, G. Dictionary of Manufactures, Mining, Machinery, and the 

Industrial Arts i2mo, i 50 

Dorr, B. F. The Surveyor's Guide and Pocket Table-book. 

i6mo, morocco, 2 00 

Down, P. B. Handy Copper Wire Table i6mo, *i 00 

Draper, C. H. Elementary Text-book of Light, Heat and Sound. . . i2mo, i 00 

Heat and the Principles of Thermo-dynamics i2mo, i 50 

Duckwall, E. W. Canning and Preserving of Food Products Svo, *5 00 

Dumesny, P., and Noyer, J. Wood Products, Distillates, and Extracts. 

Svo, *4 50 
Duncan, W. G., and Penman, D. The Electrical Equipment of Collieries. 

Svo, 
Duthie, A. L. Decorative Glass Processes. (Westminster Series.). .Svo, 

Dyson, S. S. Practical Testing of Raw Materials Svo, 

Dyson, S. S., and Clarkson, S. S. Chemical Works (In Press.) 

Eccles, R. G., and Duckwall, E. W. Food Preservatives Svo, paper 

Eddy, H. T. Researches in Graphical Statics Svo, 

Maximum Stresses under Concentrated Loads Svo, 

Edgcumbe, K. Industrial Electrical Measuring Instruments Svo, 

Eissler, M. The Metallurgy of Gold Svo, 

• The Hydrometallurgy of Copper Svo, 

The Metallurgy of Silver Svo, 

The Metallurgy of Argentiferous Lead Svo, 

Cyanide Process for the Extraction of Gold Svo, 

A Handbook on Modern Explosives Svo, 

Ekin, T. C. Water Pipe and Sewage Discharge Diagrams folio, 

Eliot, C. W., and Storer, F. H. Compendious Manual of Qualitative 

Chemical Analysis i2mo, 

Elliot, Major G. H. European Light-house Systems Svo, 

Ennis, Wm. D. Linseed Oil and Other Seed Oils Svo, 

Applied Thermodynamics Svo 

Flying Machines To-day i2mo, 

Vapors for Heat Engines i2mo, 

Erfurt, J. Dyeing of Paper Pulp. Trans, by J. Hubner Svo, 

Erskine-Murray, J. A Handbook of Wireless Telegraphy Svo, 

Evans, C. A. Macadamized Roads (In Press.) 

Ewing, A. J. Magnetic Induction in Iron Svo, *4 00 



u 


00 


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00 


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D. VAN NOSTRAND COMPANY'S SHORT TITLE CATALOG 9- 

Fairie, J. Notes on Lead Ores i2mo, *i oo 

Notes on Pottery Clays i2mo, *i 50 

Fairley, W., and Andre, Geo. J. Ventilation of Coal Mines. (Science 

Series No. 58.) i6mo, o 50 

Fairweather, W. C. Foreign and Colonial Patent Laws 8vo, *3 00 

Fanning, J. T. Hydraulic and Water-supply Engineering Svo, *5 00 

Fauth, P. The Moon in Modern Astronomy. Trans, by J. McCabe. 

Svo, *2 00 

Fay, I. W. The Coal-tar Colors Svo, *4 00 

Fernbach, R. L. Glue and Gelatine Svo, *3 00 

Chemical Aspects of Silk Manufacture i2mo, *i 00 

Fischer, E. The Preparation of Organic ComprettmiSii Tjrirj. by R. V„ 

Stanford 121m}} *i 25 

Fish, J. C. L. Lettering of Working Drawings .1 Jifelong SVji, i 00 

Fisher, H. K. C, and Darby, W. C. Submarine Cable Testing Svo, *3 50 

Fiske, Lieut. B. A. Electricity in Theory and Practice Svo, 2 50 

Fleischmann, W. The Book of the Dairy. Trans, by C. M. Aikman. Svo, 4 00 
Fleming, J. A. The Alternate-current Transformer. Two Volumes. Svo. 

Vol. I. The Induction of Electric Currents *S 00 

Vol. II. The Utilization of Induced Currents *5 00 

Propagation of Electric Currents Svo, *3 00 

Centenary of the Electrical Current Svo, *o 50 

Electric Lamps and Electric Lighting Svo, *3 00 

Electrical Laboratory Notes and Forms 4to, *5 00 

A Handbook for the Electrical Laboratory and Testing Room. Two 

Volumes Svo, each, *5 00 

Fluery, H. The Calculus Without Limits or Infinitesimals. Trans, by 

C. 0. Mailloux {In Press.) 

Flynn, P. J. Flow of Water. (Science Series No. 84.) i6mo, o 50 

Hydraulic Tables. (Science Series No. 66.) i6mo, o 50 

Foley, N. British and American Customary and Metric Measures . . folio, *3 00 
Foster, H. A. Electrical Engineers' Pocket-book. (Sixth Edition.) 

i2mo, leather, 5 00 

Engineering Valuation of Public Utilities and Factories Svo, *3 00 

Foster, Gen. J. G. Submarine Blasting in Boston (Mass.) Harbor.. . .4to, 3 50 

Fowle, F. F. Overhead Transmission Line Crossings i2mo, *i 50 

The Solution of Alternating Current Problems. Svo (In Press.) 

Fox, W. G. Transition Curves. (Science Series No. no.) i6mo, o 50 

Fox, W., and Thomas, C. W. Practical Course in Mechanical Draw- 
ing i2mo, I 25 

Foye, J. C. Chemical Problems. (Science Series No. 69.) i6mo, o 50 

Handbook of Mineralogy. (Science Series No. 86.) i6mo, o 50 

Francis, J. B. Lowell Hydraulic Experiments 4to, 15 00 

Freudemacher, P. W. Electrical Mining Installations. (Installation 

Manuals Series ) . . . i2mo, *i 00 

Fritsch, J. Manufacture of Chemical Manures. Trans, by D. Grant. 

Svo, *4 00 

Frye, A. I. Civil Engineers' Pocket-book i2mo, leather. 

Fuller, G. W. Investigations into the Purification of the Ohio River. 

4to. *io 00 

Furnell, J. Faints, Colors, Oils, and Varnishes Svo, *i 00 



10 D. VAN NOSTRAND COMPANY'S SHORT TITLE CATALOG 

Gant, L. W. Elements of Electric Traction 8vo, *2 50 

Garforth, W. E. Rules for Recovering Coal Mines after Explosions and 

Fires i2mo, leather, i 50 

Gaudard, J. Foundations. (Science Series No. 34.) i6mo, o 50 

Gear, H. B., and Williams, P. F. Electric Central Station Distribution 

Systems 8vo, *3 00 

Geerligs, H. C. P. Cane Sugar and Its Manufacture 8vo, *5 00 

Geikie, J. Structural and Field Geology ^ Svo, *4 00 

Gerber, N. Analysis of Milk, Condensed Milk, and Infants' Milk-Food. Svo, i 25 
Gerhard, W. P. Sanitation, Watersupply and Sewage Disposal of Country 

Houses i2mo, *2 00 

• Gas Lighting. (Science Series No. iii.) i6mo, o 50 

Household Wastes. (Science Series No. 97.) i6mo, o 50 

" House Drainage. (Science Series No. 63.) i6mo, o 50 

Sanitary Drainage of Buildings. (Science Series No. 93.) .... i6mo, o 50 

Gerhardi, C. W. H. Electricity Meters Svo, *4 00 

Geschwind, L. Manufacture of Alum and Sulphates. Trans, by C. 

Salter Svo, *s 00 

Gibbs, W. E. Lighting by Acetylene i2mo, *i 50 

Physics of Solids and Fluids. (Carnegie Technical School's Text- 
books.) *i 50 

Gibson, A. H. Hydraulics and Its Application Svo, *5 00 

Water Hammer in Hydraulic Pipe Lines i2mo, *2 00 

Gilbreth, F. B. Motion Study i2mo, *2 00 

Primer of Scientific Management i2mo, *i 00 

Gillmore, Gen. Q. A. Limes, Hydraulic Cements ard Mortars Svo, 4 00 

Roads, Streets, and Pavements i2mo, 2 00 

Golding, H. A. The Theta-Phi Diagram i2mo, *i 25 

Goldschmidt, R. Alternating Current Commutator Motor Svo, *3 00 

Goodchild, W. Precious Stones. (Westminster Series.) Svo, *2 00 

Goodeve, T. M. Textbook on the Steam-engine i2mo, 2 00 

Gore, G. Electrolytic Separation of Metals Svo, *3 50 

Gould, E. S. Arithmetic of the Steam-engine. . i2mo, i 00 

Calculus. (Science Series No. 112.) i6mo, o 50 

■ High Masonry Dams. (Science Series No. 22.) i6mo, o 50 

Practical Hydrostatics and Hydrostatic Formulas. (Science Series 

No. 117.) i6mo, 50 

Grant, J. Brewing and Distilling.' (Westminster Series.) Svo {In Press.) 

Gratacap, L. P. A Popular Guide to Minerals Svo (In Press.) 

Gray, J. Electrical Influence Machines i2mo, 2 00 

Greenwood, E. Classified Guide to Technical and Commercial Books. Svo, *3 00 

Gregorius, R. Mineral Waxes. Trans, by C. Salter i2mo, *3 00 

Griffiths, A. B. A Treatise on Manures i2mo, 3 00 

Dental Metallurgy Svo, *3 50 

Gross, E. Hops Svo, *4 50 

Grossman, J. Ammonia and Its Compounds i2mo, *i 25 

Groth, L. A. Welding and Cutting Metals by Gases or Electricity Svo, *3 00 

Grover, F. Modern Gas and Oil Engines Svo, *2 00 

Gruner, A. Power-loom Weaving Svo, *3 00 

Giildner, Hugo. Internal Combustion Engines. Trans, by H. Diederichs. 

4to, *I0 GO 



D. VAN NOSTRAND COMPANY'S SHORT TITLE CATALOG 11 

Gunther, C. 0. Integration i2mo, *i 25 

Gurden, R. L. Traverse Tables folio, half morocco, *7 50 

Guy, A. E. Experiments on the Flexure of Beams 8vo, *i 25 

Haeder, H. Handbook on the Steam-engine. Trans, by H. H. P. 

Powles i2mo, 

Hainbach, R. Pottery Decoration. Trans, by C. Slater i2mo, 

Haenig, A. Emery and Emery Industry 8vo, 

Hale, W. J, Calculations of General Chemistry. . i2mo. 

Hall, C. H. Chemistry of Paints and Paint Vehicles i2mo. 

Hall, R. H. Governors and Governing Mechanism i2mo. 

Hall, W. S. Elements of the Differential and Integral Calculus 8vo, 

Descriptive Geometry Svo volume and a 4to atlas, 

Haller, G. F., and Cunningham, E. T. The Tesla Coil i2mo, 

Halsey, F. A. Slide Valve Gears i2mo, 

The Use of the Slide Rule. (Science Series No. 114.) i6mo, 

Worm and Spiral Gearing. (Science Series No. 116.) i6mo, 

Hamilton, W. G. Useful Information for Railway Men i6mo, 

Hammer, W. J. Radium and Other Radio-active Substances Svo, 

Hancock, H. Textbook of Mechanics and Hydrostatics Svo, 

Hardy, E. Elementary Principles of Graphic Statics i2mo, 

Harrison, W. B. The Mechanics' Tool-book i2mo. 

Hart, J. W. External Plumbing Work Svo, 

Hints to Plumbers on Joint Wiping Svo, 

Principles of Hot Water Supply Svo, 

Sanitary Plumbing and Drainage Svo, 

Haskins, C. H. The Galvanometer and Its Uses i6mo, 

Hatt, J. A. H. The Colorist square i2mo, 

Hausbrand, E. Drying by Means of Air and Steam. Trans, by A. C. 

Wright i2mo, 

Evaporating, Condensing and Cooling Apparatus. Trans, by A. C. 

Wright ' Svo, 

Hausner, A. Manufacture of Preserved Foods and Sweetmeats. Trans. 

by A. Morris and H. Robson Svo, 

Hawke, W. H. Premier Cipher Telegraphic Code 4to, 

100,000 Words Supplement to the Premier Code 4to, 

Hawkesworth, J. Graphical Handbook for Reinforced Concrete Design. 

4to, 

Hay, A. Alternating Currents Svo, 

Electrical Distributing Networks and Distributing Lines Svo, 

Continuous Current Engineering Svo, 

Heap, Major D. P. Electrical Appliances Svo, 

Heaviside, 0. Electromagnetic Theory. Two Volumes Svo, each, 

Heck, R. C. H. The Steam Engine and Turbine Svo, 

Steam-Engine and Other Steam Motors. Two Volimies. 

Vol. I. Thermodynamics and the Mechanics Svo, 

Vol. II. Form, Construction, and Working Svo, 

Notes on Elementary Kinematics Svo, boards, 

Graphics of Machine Forces Svo, boards. 

Hedges, K. Modern Lightning Conductors Svo, 

Heermann, P. Dyers' Materials. Trans, by A. C. Wright i2mo. 



3 


00 


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00 


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00 


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25 


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50 





50 


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50 


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*2 


50 


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50 


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50 


2 


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12 D. VAN NOSTRAND COMPANY'S SHORT TITLE CATALOG 

Hellot, Macquer and D'Apligny. Art of Dyeing Wool, Silk and Cotton. 

8vo, 

Henrici, 0. Skeleton Structures 8vo, 

Hering, D. W. Physics for College Students {In Preparation.) 

Hering-Shaw, A. Domestic Sanitation and Plumbing. Two Vols. . . 8vo, 

Elementary Science Svo, 

Herrmann, G. The Graphical Statics of Mechanism. Trans, by A. P. 

Smith i2mo, 

Herzfeld, J. Testing of Yarns and Textile Fabrics. Svo, 

Hildebrandt, A. Airships, Past and Present Svo, 

Hildenbrand, B. W. Cable-Making. (Science Series No. 32.) i6mo, 

Hilditch, T. P. A Concise History of Chemistry i2mo. 

Hill, J. W. The Purification of Public Water Supplies. New Edition. 

{In Press.) 

Interpretation of Water Analysis {In Press.) 

Hiroi, I. Plate Girder Construction. (Science Series No. 95.) i6mo, 

Statically-Indeterminate Stresses i2mo, 

Hirshfeld, C. F. Engineering Thermodynamics. (Science Series No. 45.) 

i6mo, 

Hobart, H. M. Heavy Electrical Engineering Svo, 

Design of Static Transformers i2mo, 

Electricity Svo, 

— — Electric Trains Svo, 

Electric Propulsion of Ships Svo, 

Hobbs, W. R. P. The Arithmetic of Electrical Measurements i2mo, 

Hofif, J. N. Paint and Varnish Facts and Formulas i2mo, 

Hoff, Com. W. B. The Avoidance of Collisions at Sea. . . i6mo, morocco, 

Hole, W. The Distribution of Gas Svo, 

HoUey, A. L. Railway Practice folio, 

Holmes, A. B. The Electric Light Popularly Explained .... i2mo, paper, 

Hopkins, N. M. Experimental Electrochemistry . Svo, 

Model Engines and Small Boats i2mo, 

Hopkinson, J. Shoolbred, J. N., and Day, R. E. Dynamic Electricity. 

(Science Series No. 71.) i6mo. 



Metal Turning i2mo, 

Toothed Gearing i2mo, 

Houghton, C. E. The Elements of Mechanics of Materials i2mo, 

HouUevigue, L. The Evolution of the Sciences Svo, 

Howe, G. Mathematics for the Practical Man i2mo, 

Howorth, J. Repairing and Riveting Glass, China and Earthenware. 

Svo, paper, 

Hubbard, E. The Utilization of Wood- waste Svo, 

Humper, W. Calculation of Strains in Girders i2mo, 

Humphreys, A. C. The Business Features of Engineering Practice . Svo, 

Hurst, G. H. Handbook of the Theory of Color Svo, 

Dictionary of Chemicals and Raw Products Svo, 

Lubricating Oils, Fats and Greases Svo, 

Soaps Svo, 

Textile Soaps and Oils Svo, 

Hurst, H. E., and Lattey, R. T. Text-book of Physics Svo, 



*2 


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75 


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00 



D. VAN N03TRAND COMPANY^ SHORT TITLE CATALOG L3 

Hutchinson R. W., Jr. Long Distance Electric Power Transmission . i2mo, *3 oo 
Hutchinson, R. W., Jr., and Ihlseng, M. C. Electricity in Mining. . i2mo, 

(In Press) 
Hutchinson, W. B. Patents and How to Make Money Out of Them. i2mo, 

Hutton, W. S. Steam-boiler Construction 8vo, 

Practical Engineer's Handbook 8vo, 

The Works' Manager's Handbook 8vo, 

Hyde, E. W. Skew Arches. (Science Series No. 15.) i6mo, 

Induction Coils. (Science Series No. 53.) i6mo, 

Ingle, H. Manual of Agricultural Chemistry Svo, 

Innes, C. H. Problems in Machine Design i2mo, 

Air Compressors and Blowing Engines i2mo, 

Centrifugal Pumps i2mo, 

The Fan i2mo, 

Isherwood, B. F. Engineering Precedents for Steam Machinery Svo, 

Ivatts, E. B. Railway Management at Stations Svo, 

Jacob, A., and Gould, E. S. On the Designing and Construction of 

Storage Reservoirs. (Science Series No. 6.) i6mo, 

Jamieson, A. Text Book on Steam and Steam Engines Svo, 

Elementary Manual on Steam and the Steam Engine i2mo, 

Jannettaz, E. Guide to the Determination of Rocks. Trans, by G. W. 

Plympton i2mo, 

Jehl, F. Manufacture of Carbons Svo, 

Jennings, A. S. Commercial Paints and Painting. (Westminster Series.) 

Svo (In Press.) 

Jennison, F. H. The Manufacture of Lake Pigments. Svo, 

Jepson, G. Cams and the Principles of their Construction Svo, 

Mechanical Drawing Svo {In Preparation.) 

Jockin, W. Arithmetic of the Gold and Silversmith i2mo, 

Johnson, G. L. Photographic Optics and Color Photography Svo, 

Johnson, J. H. Arc Lamps and Accessory Apparatus. (Installation 

Manuals Series.) i2mo, *o 75 

Johnson, T. M. Ship Wiring and Fitting. (Installation Manuals 

Series) *o 

Johnson, W. H. The Cultivation and Preparation of Para Rubber. . Svo, 

Johnson, W. McA. The Metallurgy of Nickel {In Preparation.) 

Johnston, J. F. W,, and Cameron, C. Elements of Agricultural Chemistry 

and Geology • i2mo, 

Joly, J. Raidoactivity and Geology i2mo, 

Jones, H. C. Electrical Nature of Matter and Radioactivity i2mo, 

Jones, M. W. Testing Raw Materials Used in Paint i2mo, 

Jones, L., and Scard, F. I. Manufacture of Cane Sugar Svo, 

Joynson, F. H. Designing and Construction of Machine Gearing. . . .Svo, 
Juptner, H. F. V. Siderology: The Science of Iron Svo, 

Kansas City Bridge 4to, 6 00 

Kapp, G. Alternate Current Machinery. (Science Series No. 96.) . i6mo, o 50 

Electric Transmission of Energy i2mo, 3 50 

Keim, A. W. Prevention of Dampness in Buildings Svo, *2 00 



I 


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00 


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00 


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00 





50 





50 


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00 



14 D. VAN NOSTRAND COMPANY'S SHORT TITLE CATALOG 

Keller, S. S. Mathematics for Engineering Students. i2mo, half leather. 

Algebra and Trigonometry, with a Chapter on Vectors *i 75 

Special Algebra Edition *i oo 

Plane and Solid Geometry *i 25 

Analytical Geometry and Calculus *2 00 

Kelsey, W. R. Continuous-current Dynamos and Motors 8vo, *2 50 

Kemble, W. T., and Underbill, C. R. The Periodic Law and the Hydrogen * 

Spectrum 8vo, paper, *o 50 

Kemp, J. F. Handbook of Rocks 8vo, *i 50 

Kendall, E. Twelve Figure Cipher Code 4to, *i5 00 

Kennedy, A. B. W., and Thurston, R. H. Kinematics of Machinery. 

(Science Series No. 54.) i6mo, o 50 

Kennedy, A. B. W., Unwin, W. C, and Idell, F. E. Compressed Air. 

(Science Series No. 106.) i6mo, o 50 

Kennedy, R. Modern Engines and Power Generators. Six Volumes. 4to, 15 00 

Single Volumes each, 3 00 

Electrical Installations. Five Volumes 4to, 15 00 

Single Volumes each, 3 50 

Flying Machines; Practice and Design i2mo, *2 00 

Principles of Aeroplane Construction Svo, *i 50 

Kennelly, A.'E. Electro-dynamic Machinery Svo, i 50 

Kent, W. Strength of Materials. (Science Series No. 41.) i6mo, o 50 

Kershaw, J. B. C. Fuel, Water and Gas Analysis Svo, *2 50 

Electrometallurgy. (Westminster Series.) Svo, *2 00 

The Electric Furnace in Iron and Steel Production i2mo, *i 50 

Kinzbrunner, C. Alternate Current Windings ; Svo, *i 50 

Continuous Current Armatures Svo, *i 50 

Testing of Alternating Current Machines Svo, *2 00 

Kirkaldy, W. G. David Kirkaldy's System of Mechanical Testing 4to, 10 00 

Kirkbride, J. Engraving for Illustration Svo, *i 50 

Kirkwood, J. P. Filtration of River Waters .4to, 7 50 

Klein, J. F. Design of a High-speed Steam-engine Svo, *5 00 

Physical Significance of Entropy Svo, *i 50 

Kleinhans, F. B. Boiler Construction Svo, 3 00 

Knight, R.-Adm. A. M. Modem Seamanship Svo, *7 50 

Half morocco *9 00 

Knox, W. F. Logarithm Tables {In Preparation.) 

Knott, C. G., and Mackay, J. S. Practical Mathematics Svo, 2 00 

Koester, F. Steam-Electric Power Plants 4to, *5 00 

Hydroelectric Developments and Engineering 4to, *5 00 

Koller, T. The Utilization of Waste Products Svo, *3 50 

Cosmetics Svo, *2 50 

Kretchmar, K. Yarn and Warp Sizing Svo, *4 00 

Lambert, T. Lead and its Compounds Svo, *3 50 

Bone Products and Manures Svo, *3 00 

Lamborn, L. L. Cottonseed Products : Svo, *3 00 

Modern Soaps, Candles, and Glycerin Svo, *7 50 

Lamprecht, R. Recovery Work After Pit Fires. Trans, by C. Salter . . Svo, *4 oo 
Lanchester, F. W. Aerial Flight. Two Volumes. Svo. 

Vol. I. Aerodynamics *6 00 



D. VAN NOSTRAND COMPANY'S SHORT TITLE CATALOG 15 

Lanchester, F. W. Aerial Flight. Vol. II. Aerodonetics *6 oo 

Larner, E. T. Principles of Alternating Currents i2mo, *i 25 

Larrabee, C. S. Cipher and Secret Letter and Telegraphic Code i6mo, o 60 

La Rue, B. F. Swing Bridges. (Science Series No. 107.) i6mo, o 50 

Lassar-Cohn, Dr. Modern Scientific Chemistry. Trans, by M. M. Patti- 

son Muir i2mo, *2 00 

Latimer, L. H., Field, C. J., and Howell, J. W. Incandescent Electric 

Lighting. (Science Series No. 57.) i6mo, o 50 

Latta, M. N. Handbook of American Gas-Engineering Practice 8vo, *4 50 

American Producer Gas Practice 4to, *6 00 

Leask, A. R. Breakdowns at Sea i2mo, 2 00 

Refrigerating Machinery i2mo, 2 00 

Lecky, S. T. S. " Wrinkles " in Practical Navigation 8vo, *8 00 

Le Doux, M. Ice-Making Machines. (Science Series No. 46.) .... i6mo, o 50 

Leeds, C. C. Mechanical Drawing foi Trade Schools oblong 4to, 

High School Edition *i 25 

Machinery Trades Edition *2 00 

Lef^vre, L. Architectural Pottery. Trans, by H. K. Burd and W. M. 

Binns 4to, *7 50 

Lehner, S. Ink Manufacture. Trans, by A. Morris and H. Robson . . Svo, *2 50 

Lemstrom, S. Electricity in Agriculture and Horticulture Svo, *i 50 

Le Van, W. B. Steam-Engine Indicator. (Science Series No. 78.) . i6mo, o 50 
Lewes, V. B. Liquid and Gaseous Fuels. (Westminster Series.) . . . .8vo, *2 00 

Lewis, L. P. Railway Signal Engineering 8vo, *3 50 

Lieber, B. F. Lieber's Standard Telegraphic Code 8vo, *io 00 

' Code. German Edition , 8vo, *io 00 

Spanish Edition Svo, *io 00 

French Edition Svo, *io 00 

Terminal Index Svo, *2 50 

Lieber's Appendix folio, *i5 00 

Handy Tables 4to, *2 50 

Bankers and Stockbrokers' Code and Merchants and Shippers' Blank 

Tables Svo, *i5 00 

100,000,000 Combination Code Svo, *io 00 

Engineering Code Svo, *I2 50 

Livermore, V. P., and Williams, J. How to Become a Competent Moior- 

man 1 2mo, *i 00 

Livingstone, R. Design and Construction of Commutators Svo, *2 25 

Lobben, P. Machinists' and Draftsmen's Handbook Svo, 2 50 

Locke, A. G. and C. G. Manufacture of Sulphuric Acid Svo, 10 00 

Lockwood, T. D. Electricity, Magnetism, and Electro-telegraph .... Svo, 2 50 

Electrical Measurement and the Galvanometer. i2mo, i 50 

Lodge, 0. J. Elementary Mechanics i2mo, i 50 

Signalling Across Space without Wires Svo, *2 00 

Lord, R. T. Decorative and Fancy Fabrics Svo, *3 50 

Loring, A. E. A Handbook of the Electromagnetic Telegraph i6mo, o 50 

Handbook. (Science Series No. 39.) i6mo, o 50 

Loewenstein, L. C, and Crissey, C. P. Centrifugal Pumps *4 50 

Lucke, C. E. Gas Engine Design Svo, *3 00 

Power Plants: their Design, Eflficiency, and Power Costs. 2 vols. 

{In Preparation.) 



16 D. VAN NOSTRAND COMPANY'S SHORT TITLE CATALOG 

Lunge, G. Coal-tar and Ammonia. Two Volumes 8vo, *i5 oa 

Manufacture of Sulphuric Acid and Alkali. Four Volumes 8vo, 

Vol. I. Sulphuric Acid. In two parts *i5 oo 

Vol. II. Salt Cake, Hydrochloric Acid and Leblanc Soda. In two 

parts *i5 oo 

Vol. III. Ammonia Soda *io oo 

Vol. IV. Electrolytic Methods (In Press.) 

Technical Chemists' Handbook i2mo, leather, *3 50 

Technical Methods of Chemical Analysis. Trans, by C. A. Keane. 

in collaboration with the corps of specialists. 

Vol. I. In two parts 8vo, *i5 00 

Vol. n. In two parts Svo, *i8 oo 

Vol. Ill (In Preparation.) 

Lupton, A., Parr, G. D. A., and Perkin, H. Electricity as Applied to 

Mining 8vo, *4 50 

Luquer, L. M. Minerals in Rock Sections 8vo, *i 50 

Macewen, H. A. Food Inspection - 8vo, *2 50 

Mackenzie, N. F. Notes on Irrigation Works 8vo, *2 50 

Mackie, J. How to Make a Woolen Mill Pay 8vo, *2 00 

Mackrow, C. Naval Architect's and Shipbuilder's Pocket-book. 

i6mo, leather, 5 00 

Maguire, Wm. R. Domestic Sanitary Drainage and Plumbing 8vo, 4 00 

Mallet, A. Compound Engines. Trans, by R. R. Buel. (Science Series 

No. 10.) i6mo, 

Mansfield, A. N. Electro-magnets. (Science Series No. 64.) i6mo, o 50 

Marks, E. C. R. Construction of Cranes and Lifting Machinery. . . . i2mo, *i 50 

Construction and Working of Pumps i2mo, *i 50 

Manufacture of Iron and Steel Tubes i2mo, *2 00 

Mechanical Engineering Materials i2mo, *i 00 

Marks, G. C. Hydraulic Power Engineering Svo, 3 50 

Inventions, Patents and Designs i2mo, *i 00 

Marlow, T. G. Drying Machinery and Practice 8vo, *5 00 

Marsh, C. F. Concise Treatise on Reinforced Concrete Svo, *2 50 

Marsh, C. F., and Dunn, W. Reinforced Concrete 4to, *5 00 

Marsh, C. F., and Dunn, W. Manual of Reinforced Concrete and Con- 
crete Block Construction i6mo, morocco, *2 50 

Marshall, W. J., and Sankey, H. R. Gas Engines. (Westminster Series.) 

Svo, *2 00 

Martin. G, Triimiphs and Wonders of Modem Chemistry Svo, *2 00 

Massie, W. W., and Underhill, C. R. Wireless Telegraphy and Telephony. 

i2mo, *i 00 
Matheson, D. Australian Saw-Miller's Log and Timber Ready Reckoner. 

i2mo, leather, 

Mathot, R. E. Internal Combustion Engines Svo, 

Maurice, W. Electric Blasting Apparatus and Explosives Svo, 

Shot Firer's Guide Svo, 

Maxwell, J. C. Matter and Motion. (Science Series No. 36.) i6mo. 

Maxwell, W. H., and Brown, J. T. Encyclopedia of Municipal and Sani- 
tary Engineering 4*0, 

Mayer, A. M. Lecture Notes on Physics Svo, 



I 


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50 


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D. VAN NOSTRAND COMPANY'S SHORT TITLE CATALOG 17 

McCullough, R. S. Mechanical Theory of Heat 8vo, 

Mcintosh, J. G. Technology of Sugar 8vo, 

Industrial Alcohol 8vo, 

Manufacture of Varnishes and Kindred Industries. Three Volumes. 

Svo. 

Vol. I. Oil Crushing, Refining and Boiling 

Vol. II. Varnish Materials and Oil Varnish Making 

Vol. III. Spirit Varnishes an'd Materials *4 

McKnight, J. D., and Brown, A. W. Marine Multitubular Boilers *i 

McMaster, J. B. Bridge and Tunnel Centres. (Science Series No. 20.) 

i6mo, 

McMechen, F.L. Tests for Ores, Minerals and Metals i2mo, 

McNeUl, B. McNeiU's Code 8vo, 

McPherson, J. A. Water- works Distribution 8vo, 

Melick, C. W. Dairy Laboratory Guide i2mo, 

Merck, E. Chemical Reagents; Their Purity and Tests 8vo, 

Merritt, Wm. H. Field Testing for Gold and Silver i6mo, leather, 

Meyer, J. G. A., and Pecker, C. G. Mechanical Drawing and Machine 

Design 4to, 

Michell, S. Mine Drainage 8vo, 

Mierzinski, S. Waterproofing of Fabrics. Trans, by A. Morris and H. 

Robson 8vo, 

Miller, E. H. Quantitative Analysis for Mining Engineers 8vo, 

Miller, G. A. Determinants. (Science Series No. 105.) i6mo, 

Milroy, M. E. W. Home Lace-making i2mo, 

Minifie, W. Mechanical Drawing Svo, 

Mitchell, C. A., and Prideaux, R. M. Fibres Used in Textile and Allied 

Industries 8vo, 

Modern Meteorology i2mo, 

Monckton, C. C. F. Radiotelegraphy. (Westminster Series.) 8vo, 

Monteverde, R. D. Vest Pocket Glossary of English-Spanish, Spanish- 
English Technical Terms 64mo, leather, *i 00 

Moore, E. C. S. New Tables for the Complete Solution of Ganguillet and 

Kutter's Formula. 8vo, 

Morecroft, J. H., and Hehre, F. W. Short Course in Electrical Testing. 

8vo, 
Moreing, C. A., and Neal, T. New General and Mining Telegraph Code, Svo, 

Morgan, A. P. Wireless Telegraph Apparatus for Amateurs i2mo, 

Moses, A. J. The Characters of Crystals Svo, 

Moses, A. J., and Parsons, C. L. Elements of Mineralogy Svo, 

Moss, S. A. Elements of Gas Engine Design. (Science Series No.i2i.)i6mo, 

The Lay-out of Corliss Valve Gears. (Science Series No. 119.). i6mo, 

MuUin, J. P. Modern Moulding and Pattern-making i2mo, 

Munby, A. E. Chemistry and Physics of Building Materials. (Westmin- 
ster Series.) Svo, 

Murphy, J. G. Practical Mining i6mo, 

Murray, J. A. Soils and Manures. (Westminster Series.) Svo, *2 00 

Naquet, A. Legal Chemistry ; . . i2mo, 2 00 

Nasmith, J. The Student's Cotton Spinning Svo, 3 00 

Recent Cotton Mill Construction i2mo, 2 00 



3 


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18 D. VAN NOSTRAND COMPANY'S SHORT TITLE CATALOG 

Neave, G. B,. and Heilbron, I. M. Identification of Organic Compounds. 

i2mo, *i 25 

Neilson, R. M. Aeroplane Patents 8vo, *2 oa 

Nerz, F. Searchlights. Trans, by C. Rodgers 8vo, *3 00 

Nesbit, A. F. Electricity and Magnetism {In Preparation.) 

Neuberger, H., and Noalhat, H. Technology of Petroleum. Trans, by J. 

G. Mcintosh 8vo, *io 00 

Newall, J. W. Drawing, Sizing and Cutting Cevel-gears Svo, i 50 

Nicol, G. Ship Construction and Calculations Svo, *4 50 

Nipher, F. E. Theory of Magnetic Measurements i2mo, i 00 

Nisbet, H. Grammar of Textile Design Svo, *3 00 

Nolan, H. The Telescope. (Science Series No. 51.) i6mo, o 5a 

Noll, A. How to Wire Buildings i2mo, i 50 

Nugent, E. Treatise on Optics i2mo, i 50 

O'Connor, H. The Gas Engineer's Pocketbook i2mo, leather, 3 50 

Petrol Air Gas . i2mo, *o 75: 

Ohm, G. S., and Lockwood, T. D. Galvanic Circuit. Translated by 

William Francis. (Science Series No. 102.) i6mo, o 50 

Olsen, J. C. Text-book of Quantitative Chemical Analysis Svo, *4 oa 

Olsson, A. Motor Control, in Turret Turning and Gun Elevating. (U. S. 

Navy Electrical Series, No. i.) i2mo, paper, *o 5a 

Oudin, M. A. Standard Polyphase Apparatus and Systems Svo, *3 00 

Palaz, A. Industrial Photometry. Trans, by G. W. Patterson, Jr. . . Svo, *4 00 

Pamely, C. Colliery Manager's Handbook Svo, *io oa 

Parr, G. D. A. Electrical Engineering Measuring Instruments Svo, *3 50 

Parry, E. J. Chemistry of Essential Oils and Artificial Perfumes .... Svo, *5 oa 

Foods and Drugs. Two Volumes Svo, 

Vol. I. Chemical and Microscopical Analysis of Foods and Drugs. **j 5a 

Vol. n. Sale of Food and Drugs Act *3 00 

Parry, E. J., and Coste, J. H. Chemistry of Pigments Svo, *4 50 

l^arry, L. A. Risk and Dangers of Various Occupations Svo, *3 00 

Parshall, H. F., and Hobart, H. M. Armature Windings 4to, *7 50 

Electric Railway Engineering 4to, *io 00 

Parshall, H. F., and Parry, E. Electrical Equipment of Tramways.. . . {In Press.) 

Parsons, S. J. Malleable Cast Iron Svo, *2 5a 

Partington, J. R. Higher Mathematics for Chemical Students. .i2mo, *2 00 

Passmore, A. C. Technical Terms Used in Architecture Svo, *3 50 

Patterson, D. The Color Printing of Carpet Yarns Svo, *3 50 

Color Matching on Textiles Svo, *3 00 

The Science of Color Mixing Svo, *3 00 

Paulding, C. P. Condensation of Steam in Covered and Bare Pipes. .Svo, *2 00 

Transmission of Heat through Cold-storage Insulation i2mo, *i 00 

Peirce, B. System of Analytic Mechanics 4to, 10 00 

Pendred, V. The Railway Locomotive. (Westminster Series.) Svo, *2 00 

Perkin, F. M. Practical Methods of Inorganic Chemistry i2mo, *i oa 

Perrigo, 0. E. Change Gear Devices Svo, i 00 

Perrine, F. A. C. Conductors for Electrical Distribution Svo, *3 50 

Perry, J. Applied Mechanics Svo, *2 50 

Petit, G. White Lead and Zinc White Paints Svo, *i 5a 



D. VAN NOSTRAND COMPANY'S SHORT TITLE CATALOG 19 

Petit, R. How to Build an Aeroplane. Trans, by T. O'B. Hubbard, and 

J. H. Ledeboer 8vo, *i 50 

Pettit, Lieut. J. S. Graphic Processes. (Science Series No. 76.) . . . i6mo, o 50 
Philbrick, P. H. Beams and Girders. (Science Series No. 88.) . . . i6mo, 

Phillips, J. Engineering Chemistry 8vo, *4 50 

Gold Assaying 8vo, *2 50 

Dangerous Goods 8vo, 3 50 

Phin, J. Seven Follies of Science i2mo, *i 25 

Pickworth, C. N. The Indicator Handbook. Two Volumes. . i2mo, each, i 50 

Logarithms for Beginners i2mo, boards, o 50 

The Slide Rule i2mo, i 00 

Plattner's Manual of Blow-pipe Analysis. Eighth Edition, revised. Trans. 

by H. B. Cornwall 8vo, *4 00 

Plympton, G. W. The Aneroid Barometer. (Science Series No. 35.) i6mo, o 50 

How to become an Engineer. (Science Series No. 100.) i6mo, o 50 

Van Nostrand's Table Book. (Science Series No. 104.) i6mo, o 50 

Pochet, M. L. Steam Injectors. Translated from the French. (Science 

Series No. 29.). i6mo, 50 

Pocket Logarithms to Four Places. (Science Series No. 65.) i6mo, o 50 

leather, i 00 

PoUeyn, F. Dressings and Finishings for Textile Fabrics 8vo, *3 00 

Pope, F. L. Modern Practice of the Electric Telegraph 8vo, i 50 

Popplewell, W. C. Elementary Treatise on Heat and Heat Engines. . i2mo, *3 00 

Prevention of Smoke 8vo, *3 50 

Strength of Materials 8vo, *i 75 

Potter, T. Concrete 8vo, *3 00 

Practical Compounding of Oils, Tallow and Grease 8vo, *3 50 

Practical Iron Founding i2mo, i 50 

Pray, T., Jr. Twenty Years with the Indicator. 8vo, 2 50 

Steam Tables and Engine Constant 8 vo, 2 00 

Calorimeter Tables .8vo, i 00 

Preece, W. H. Electric Lamps (In Press.) 

Prelini, C. Earth and Rock Excavation 8vo, *3 00 

Graphical Determination of Earth Slopes 8vo, *2 00 

Tunneling. New Edition 8vo, *3 00 

Dredging. A Practical Treatise 8vo, *3 00 

Prescott, A. B. Organic Analysis 8vo, 5 00 

Prescott, A. B., and Johnson, 0. C. Qualitative Chemical Analysis. . . 8vo, *3 50 
Prescott, A. B., and Sullivan, E. C. First Book in Qualitative Chemistry. 

i2mo, *i 50 

Pritchard, 0. G. The Manufacture of Electric-light Carbons . . 8vo, paper, *o 60 
PuUen, W. W. F. Application of Graphic Methods to the Design of 

Structures i2mo, *2 50 

Injectors: Theory, Construction and Working i2mo, *i 50 

Pulsifer, W. H. Notes for a History of Lead 8vo, 4 00 

Purchase, W. R. Masonry i2mo, *3 00 

Putsch, A. Gas and Coal-dust Firing 8vo, *3 00 

Pynchon, T. R. Introduction to Chemical Physics 8vo, 3 00 

Rafter G. W. Mechanics of Ventilation. (Science Series No. 33.) . i6mo, o 50 
Potable Water, (Science Series No. 103.) i6mo, o 50 






50 


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20 D VAN NOSTRAND COMPANY'S SHORT TITLE CATALOG 

Rafter, G. W. Treatment of Septic Sewage. (Science Series No. ii8.) 

i6mo, 
Rafter, G. W., and Baker, M. N. Sewage Disposal in the United States . 4to, 

Raikes, H. P. Sewage Disposal Works 8vo, 

Railway Shop Up-to-Date 4to, 

Ramp, H. M. Foundry Practice {In Press.) 

Randall, P. M. Quartz Operator's Handbook. i2mo, 

Randau, P. Enamels and Enamelling 8vo, 

Rankine, W. J. M. Applied Mechanics Svo, 

Civil Engineering Svo, 

Machinery and Millwork Svo, 

The Steam-engine and Other Prime Movers Svo, 

Useful Rules and Tables Svo, 

Rankine, W. J. M., and Bamber, E. F. A Mechanical Text-book. . . Svo, 
Raphael, F. C. Localization of Faults in Electric Light and Power Mains. 

Svo, 

Rathbone, R. L. B. Simple Jewellery Svo, 

Rateau, A. Flow of Steam through Nozzles and Orifices. Trans, by H. 

B. Brydon Svo, 

Rausenberger, F. The Theory of the Recoil of Guns Svo, 

Rautenstrauch, W. Notes on the Elements of Machine Design. Svo, boards, 
Rautenstrauch, W., and Williams, J. T. Machine Drafting and Empirical 
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Part I. Machine Drafting Svo, *i 23 

Part II. Empirical Design {In Preparation.) 

Raymond, E. B. Alternating Current Engineering i2mo, 

Rayner, H. Silk Throwing and Waste Silk Spinning Svo, 

Recipes for the Color, Paint, Varnish, Oil, Soap and Drysaltery Trades . Svo, 

Recipes for Flint Glass Making i2mo, 

Redwood, B. Petroleum. (Science Series No. 92.) i6mo. 

Reed's Engineers' Handbook Svo, 

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Marine Boilers i2mo, 

Reinhardt, C. W. Lettering for Draftsmen, Engineers, and Students. 

oblong 4to, boards, 

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Reiser, F. Hardening and Tempering of Steel. Trans, by A. Morris and 

H. Robson i2mo, *2 05 

Reiser, N. Faults in the Manufacture of Woolen Goods. Trans, by A. 

Morris and H. Robson Svo, 

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Renwick, W. G. Marble and Marble Working Svo, 

Reynolds, O., and Idell, F. E. Triple Expansion Engines. (Science 

Series No. 99.) i6mo, 

Rhead, G. F. Simple Structural Woodwork i2mo. 

Rice, J. M., and Johnson, W. W. A New Method of Obtaining the Differ- 
ential of Functions i2mo, 

Richardson, J. The Modern Steam Engine Svo, 

Richardson, S. S. Magnetism and Electricity i2mo, 

Rideal, S. Glue and Glue Testing Svo, 



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D. VAN NOSTRAND COMPANY'S SHORT TITLE CATALOG 21 

Rings, F. Concrete in Theory and Practice i2mo, *2 50 

Ripper, W. Course of Instruction in Machine Drawing folio, *6 00 

Roberts, F. C. Figure of the Earth. (Science Series No. 79.) i6mo, o 50 

Roberts, J., Jr. Laboratory Work in Electrical Engineering 8vo, *2 00 

Robertson, L. S. Water-tube Boilers 8vo, 3 00 

Robinson, J. B. Architectural Composition 8vo, *2 50 

Robinson, S. W. Practical Treatise on the Teeth of Wheels. (Science 

Series No. 24.) i6nio, o 50 

Railroad Economics. (Science Series No. 59.) i6mo, 50 

Wrought Iron Bridge Members. (Science Series No. 60.) i6mo, o 50 

Robson, J. H. Machine Drawing and Sketching .8vo, *i 50 

Roebling, J A. Long and Short Span Railway Bridges folio, 25 00 

Rogers, A. A Laboratory Guide of Industrial Chemistry i2mo, *i 50 

Rogers, A., and Aubert, A. B. Industrial Chemistry {In Press.) 

Rogers, F. Magnetism of Iron Vessels. (Science Series No. 30.) . . i6mo, o 50 

Rollins, W. Notes on X-Light 8vo, *5 00 

Rose, J. The Pattern-makers' Assistant 8vo, 2 50 

Key to Engines and Engine-running i2mo, 2 50 

Rose, T. K. The Precious Metals. (Westminster Series.) 8vo, *2 00 

Rosenhain, W. Glass Manufacture. (Westminster Series.) 8vo, *2 00 

Ross, W. A. Plowpipe in Chemistry and Metallurgy i2mo, *2 00 

Rossiter, J. T. Steam Engines. (Westminster Series.). . . .8vo (In Press.) 

Pumps and Pumping Machinery. (Westminster Series.). .8 vo {In Press.) 

Roth. Physical Chemistry 8vo, *2 00 

Rouillion, L. The Economics of Manual Training 8vo, 2 00 

Rowan, F. J. Practical Physics of the Modern Steam-boiler 8vo, 7 50 

Rowan, F. J., and Idell, F. E. Boiler Incrustation and Corrosion. 

(Science Series No. 27.) i6mo, o 50 

Roxburgh, W. General Foundry Practice 8vo, *3 50 

Ruhmer, E. Wireless Telephony. Trans, by J. Erskine-Murray . . . .8vo, *3 50 

Russell, A. Theory of Electric Cables and Networks 8vo, *3 op 

Sabine, R. History and Progress of the Electric Telegraph i2mo, i 25 

Saeltzer A. Treatise on Acoustics i2mo, i 00 

Salomons, D. Electric Light Installations. i2mo. 

Vol. I. The Management of Accumulators 2 50 

Vol. 11. Apparatus 2 25 

Vol. III. Applications '. i 50 

Sanford, P. G. Nitro-explosives 8vo, *4 00 

Saunders, C. H. Handbook of Practical Mechanics i6mo, i 00 

leather, i 25 

Saunnier, C. Watchmaker's Handbook i2mo, 3 00 

Sayers^ H. M. Brakes for Tram Cars 8vo, *i 25 

Scheele, C. W. Chemical Essays 8vo, *2 00 

Schellen, H. Magneto-electric and Dynamo-electric Machines 8vo, 5 00 

Scherer, R. Casein. Trans, by C. Salter 8vo, *3 00 

Schidrowitz, P. Rubber, Its Production and Industrial Uses 8vo, *5 00 

Schmall, C. N. First Course in Analytic Geometry, Plane and Solid. 

i2mo, half leather, *i 75 

Schmall, C. N., and Shack, S. M. Elements of Plane Geometry. . . . i2mo, *i 25 

Schmeer, L. Flow of Water 8vo, *3 00 



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22 D. VAN NOSTRAND COMPANY'S SHORT TITLE CATALOG 

Schumann, F. A Manual of Heating and Ventilation i2mo, leather, 

Schwarz, E. H. L. Causal Geology 8vo, 

Schweizer, V., Distillation of Resins 8vo, 

Scott, W. W. Qualitative Analysis. A Laboratory Manual 8vo, 

Scribner, J. M. Engineers' and Mechanics' Companion . . . i6mo, leather, 

Searle, A. B. Modern Brickmaking Bvo, 

Searle, G. M. " Sumners' Method." Condensed and Improved. (Science 

Series No. 124.) i6mo, 

Seaton, A. E. Manual of Marine Engineering Bvo, 

Seaton, A. E., and Rounthwaite, H. M. Pocket-book of Marine Engineer- 
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Seeligmann, T., Torrilhon, G. L., and Falconnet, H. India Rubber and 

Gutta Percha. Trans, by J. G. Mcintosh 8vo, 

Seidell, A. Solubilities of Inorganic and Organic Substances Bvo, 

Sellew, W. H. Steel Rails 4to (/n Press.) 

Senter, G. Outlines of Physical Chemistry i2mo. 

Sever, G. F. Electric Engineering Experiments 8vo, boards, 

Sever, G. F., and Townsend, F. Laboratory and Factory Tests in Electrical 

Engineering , Bvo, 

Sewall, C. H. Wireless Telegraphy Bvo, 

Lessons in Telegraphy i2mo, 

Sewell, T. Elements of Electrical Engineering 8vo, 

The Construction of Dynamos Bvo, 

Sexton, A. H. Fuel and Refractory Materials i2mo, 

• Chemistry of the Materials of Engineering i2mo, 

— — Alloys (Non- Ferrous) gvo, 

The Metallurgy of Iron and Steel Bvo, 

Seymour, A. Practical Lithography Bvo, 

Modern Printing Inks ...,.' Bvo, 

Shaw, Henry S. H. Mechanical Integrators. (Science Series No. 83.) 

i6mo, 

Shaw, P. E. Course of Practical Magnetism and Electricity Bvo, 

Shaw, S. History of the Staffordshire Potteries Bvo, 

Chemistry of Compounds Used in Porcelain Manufacture Bvo, 

Shaw, W. N. Forecasting Weather Bvo {In Press.) 

Sheldon, S., and Hausmann, E. Electric Traction i2mo, 

Direct Current Machines . . i2mo, 

Alternating Current Machines i2mo, 

Electric Traction and Transmission Engineering Bvo, 

Sherriff, F. F. Oil Merchants' Manual i2mo. 

Shields, J. E. Notes on Engineering Construction i2mo. 

Shock, W. H. Steam Boilers 4to, half morocco, 

Shreve, S. H. Strength of Bridges and Roofs Bvo, 

Shunk, W. F. The Field Engineer i2mo, morocco, 

Simmons, W. H., and Appleton, H. A. Handbook of Soap Manufacture. 

Bvo, 

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Simms, F. W. The Principles and Practice of Leveling Bvo, 

Practical Tunneling Bvo, 

Simpson, G. The Naval Constructor i2mo, morocco, 

Sinclair, A. Development of the Locomotive Engine . . . Bvo, half leather. 



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D. VAN NOSTRAND COMPANY'S SHORT TITLE CATALOG 23 

Sinclair, A. Twentieth Century Locomotive 8vo, half leather, 

Sindall, R. W. Manufacture of Paper. (Westminster Series.) 8vo, 

Sloane, T. O'C. Elementary Electrical Calculations i2mo. 

Smith, C. A. M. Handbook of Testing, MATERIALS 8vo, 

Smith, C. A. M., and Warren, A. G. New Steam Tables Svo, 

Smith, C. F. Practical Alternating Currents and Testing Svo, 

Practical Testing of Dynamos and Motors Svo, 

Smith, F. E. Handbook of General Instruction for Mechanics. . . . i2mo. 

Smith, J. C. Manufacture of Paint Svo, 

Smith, R. H. Principles of Machine Work i2mo, 

Elements of Machine Work i2mo, 

Smith, W. Chemistry of Hat Manufacturing i2mo, 

Snell, A. T. Electric Motive Power Svo, 

Snow, W. G. Pocketbook of Steam Heating and Ventilation. {In Press.) 
Snow, W. G., and Nolan, T. Ventilation of Buildings. (Science Series 

No. 5.).. , i6mo, 

Soddy, F. Radioactivity Svo, 

Solomon, M. Electric Lamps. (Westminster Series.) Svo, 

Sothern, J. W. The Marine Steam Turbine Svo, 

Soxhlet, D. H. Dyeing and Staining Marble. Trans, by A. Morris and 

H. Robson Svo, 

Spang, H. W. A Practical Treatise on Lightning Protection i2mo, 

Spangenburg, L. Fatigue of Metals. Translated by S. H. Shreve. 

(Science Series No. 23.) i6mo, o 50 

Specht, G. J., Hardy, A. S., McMaster, J.B ., and Walling. Topographical 

Surveying. (Science Series No. 72.) i6mo, 

Speyers, C. L. Text-book of Physical Chemistry Svo, 

Stahl, A. W. Transmission of Power. (Science Series No. 2S.) . . . i6mo, 

Stahl, A. W., and Woods, A. T. Elementary Mechanism i2mo, 

Staley, C, and Pierson, G. S. The Separate System of Sewerage. . . .Svo, 

Standage, H. C. Leatherworkers' Manual Svo, 

Sealing Waxes, Wafers, and Other Adhesives Svo, 

Agglutinants of all Kinds for all Purposes i2mo, 

Stansbie, J. H. Iron and Steel. (Westminster Series.) Svo, 

Steinman, D. B. Suspension Bridges and Cantilevers. (Science Series 

No. 127) 

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Stevenson, J. L. Blast-Furnace Calculations i2mo, leather, 

Stewart, A. Modern Polyphase Machinery i2mo, 

Stewart, G. Modern Steam Traps i2mo, 

Stiles, A. Tables for Field Engineers. , i2mo, 

Stillman, P. Steam-engine Indicator i2mo, 

Stodola, A. Steam Turbines. Trans, by L. C. Loewenstein Svo, 

Stone, H. The Timbers of Commerce Svo, 

Stone, Gen. R. New Roads and Road Laws i2mo, 

Stopes, M. Ancient Plants Svo, 

The Study of Plant Life Svo, 

Sudborough, J. J., and James, T. C. Practical Organic Chemistry. . i2mo, 

Suffling, E. R. Treatise on the Art of Glass Painting Svo, 

Swan, K. Patents, Designs and Trade Marks. (Westminster Series.). Svo, 
Sweet, S. H. Special Report on Coal Svo, 






50 


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24 D. VAN NOSTRAND COMPANY'S SHORT TITLE CATALOG 

Swinburne, J., Wordingham, C. H., and Martin, T. C. Eletcric Currents. 

(Science Series No. 109.) i6mo, o 50 

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Tailfer, L. Bleaching Linen and Cotton Yarn and Fabrics 8vo, *5 00 

Tate, J. S. Surcharged and Different Forms of Retaining-walls. (Science 

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Templeton, W. Practical Mechanic's Workshop Companion. 

i2mo, morocco, 2 00 
Terry, H. L. India Rubber and its Manufacture. (Westminster Series.) 

8vo, *2 00 

Thayer, H. R. Design of Structures {In Press.) 

Thiess, J. B. and Joy, G. A. Toll Telephone Practice (In Press.) 

Thom, C, and Jones, W. H. Telegraphic Connections oblong i2mo, i 50 

Thomas, C. W. Paper-makers' Handbook (In Press.) 

Thompson, A. B. Oil Fields of Russia 4to, *7 50 

Petroleum Mining and Oil Field Development 8vo, *5 00 

Thompson, E. P. How to Make Inventions Svo, o 50 

Thompson, S. P. Dynamo Electric Machines. (Science Series No. 75.) 

i6mo, o 50 

Thompson, W. P. Handbook of Patent Law of All Countries i6mo, i 50 

Thornley, T. Cotton Combing Machines Svo, *3 00 

Cotton Spinning. Svo. 

First Year *i 50 

Second Year. *2 50 

Third Year *2 50 

Thurso, J. W. Modern Turbine Practice Svo, *4 00 

Tidy, C. Meymott. Treatment of Sewage. (Science Series No. 94.). 

i6mo, o 50 

Tinney, W. H. Gold-mining Machinery Svo, *3 00 

Titherley, A. W. Laboratory Course of Organic Chemistry Svo, *2 00 

Toch, M. Chemistry and Technology of Mixed Paints Svo, *3 00 

Materials for Permanent Painting i2mo, *2 00 

Todd, J., and Whall, W. B. Practical Seamanship Svo, *7 50 

Tonge, J. Coal. (Westminster Series.) Svo, *2 00 

Townsend, F. Alternating Current Engineering Svo, boards *o 73 

Townsend, J. Ionization of Gases by Collision Svo, *i 25 

Transactions of the American Institute of Chemical Engineers. Svo. 

Vol. L 1908 *6 00 

Vol. II. 1909 *6 00 

Vol. III. 1910 *6 00 

Traverse Tables. (Science Series No. 115.) i6mo, 

morocco, 
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i6mo, 

Trowbridge, W. P. Turbine Wheels. (Science Series No. 44.) i6mo. 

Tucker, J. H. A Manual of Sugar Analysis Svo, 

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Tunner, P. A. Treatise on Roll-turning. Trans, by J. B. Pearse. 

Svo, text and folio atlas, 
Turbayne, A. A. Alphabets and Numerals 4to» 






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TurnbuU, Jr., J., and Robinson, S. W. A Treatise on the Compound 

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Turrill, S. M. Elementary Course in Perspective i2mo, *i 25 

Underbill, C. R. Solenoids, Electromagnets and Electromagnetic Wind- 
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Urquhart, J. W. Electric Light Fitting i2mo, 2 do 

Electro-plating i2mo, 2 00 

Electrotyping i2mo, 2 00 

Electric Ship Lighting i2mo, 3 00 

Universal Telegraph Cipher Code i2mo, i 00 

Vacher, F. Food Inspector's Handbook i2mo, *2 50 

Van Nostrand's Chemical Annual. Second issue 1909. , i2mo, *2 50 

Year Book of Mechanical Engineering Data. First issue 191 2 . . . {In Press.) 

Van Wagenen, T. F. Manual of Hydraulic Mining i6mo, i 00 

Vega, Baron Von. Logarithmic Tables 8vo, half morocco, 2 50 

Villon, A. M. Practical Treatise on the Leather Industry. Trans, by F. 

T. Addyman Svo, *io 00 

Vincent, C. Ammonia and its Compounds. Trans, by M. J. Salter .. Svo, *2 00 

Volk, C. Haulage and Winding Appliances Svo, *4 00 

Von Georgievics, G. Chemical Technology of Textile Fibres. Trans, by 

C. Salter Svo, *4 50 

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Vose, G. L. Graphic Method for Solving Certain Questions in Arithmetic 

and Algebra. (Science Series No. 16.) i6mo, o 50 

Wabner, R. Ventilation in Mines. Trans, by C. Salter Svo, *4 50 

Wade, E. J. Secondary Batteries Svo, *4 00 

Wadsworth, C. Primary Battery Ignition i2mo {In Press.) 

Wagner, E. Preserving Fruits, Vegetables, and Meat i2mo, *2 50 

Walker, F. Aerial Navigation Svo, 2 00 

Dynamo Building. (Science Series No. 98.) i6mo, o 50 

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Walker, S. F. Steam Boilers, Engines and Turbines Svo, 3 00 

Refrigeration, Heating and Ventilation on Shipboard i2mo, *2 00 

Electricity in Mining Svo, *3 50 

Walker, W. H. Screw Propulsion Svo, o 75 

Wallis-Tayler, A. J. Bearings and Lubrication Svo, *i 50 

Modern Cycles Svo, 4 00 

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Wanklyn, J. A. Water Analysis i2mo, 2 00 

Wansbrough, W. D. The A B C of the Differential Calculus . . i2mo, *i 50 

Shde Valves i2mo, *2 00 

Ward, J. H. Steam for the Million Svo, i 00 

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26 D, VAN NOSTRAND COMPANY'S SHORT TITLE CATALOG 

Waring, Jr., G. E. Modern Methods of Sewage Disposal i2mo, 2 00 

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Warren, F. D. Handbook on Reinforced Concrete i2mo, *2 50 

Watkins, A. Photography. (Westminster Series.) 8vo, *2 oo 

Watson, E. P. Small Engines and Boilers i2mo, i 25 

Watt, A. Electro-plating and Electro-refining of Metals 8vo, *4 5a 

Electro-metallurgy i2mo, i oa 

The Art of Soap-making 8vo, 3 oa 

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Weale's Scientific and Technical Series. (Complete list sent on applica- 
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Weather and Weather Instruments i2mo, i 00 

paper, o 50 

Webb, H. L. Guide to the Testing of Insulated Wires and Cables. . i2mo, i 00 

Webber, W. H. Y. Town Gas. (Westminster Series.) 8vo, *2 00 

Weisbach, J. A Manual of Theoretical Mechanics 8vo, *6 00 

sheep, *7 50 

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Weston, E. B. Loss of Head Due to Friction of Water in Pipes . . . i2mo, *i 50 

Weymouth, F. M. Drum Armatures and Commutators 8vo, *3 oa 

Wheatley, O. Ornamental Cement Work {In Press.) 

Wheeler, J. B. Art of War i2mo, i 75 

Field Fortifications i2mo, i 75 

Whipple, S. An Elementary and Practical Treatise on Bridge Building. 

8vo, 3 00 

Whithard, P. Illuminating and Missal Painting i2mo, i 5a 

Wilcox, R. M. Cantilever Bridges. (Science Series No. 25.) i6mo, o 50 

Wilkinson, H. D. Submarine Cable Laying and Repairing Svo, *6 oa 

Williams, A. D., Jr., and Hutchinson, R. W. The Steam Turbine {In Press.) 

Williamson, R. S. On the Use of the Barometer 4to, 15 oa 

Practical Tables in Meteorology and Hypsometery 4to, 2 5a 

WiUson, F. N. Theoretical and Practical Graphics 4to, *4 oa 

Wimperis, H. E. Internal Combustion Engine Svo, *3 00 

Winchell, N. H., and A. N. Elements of Optical Mineralogy Svo, *3 5a 

Winkler, C, and Lunge, G. Handbook of Technical Gas-Analysis ... Svo, 4 00 

Winslow, A. Stadia Surveying. (Science Series No. 77.) i6mo, o 5a 

Wisser, Lieut. J. P. Explosive Materials. (Science Series No. 70.). 

i6mo, o 50 

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Wood, De V. Luminiferous Aether. (Science Series No. 85.). . . . i6mo, o 50 
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Svo, half morocco, 4 00 

Worden, E. C. The Nitrocellulose Industry. Two Volumes Svo, *io oa 

Wright, A. C. Analysis of Oils and Allied Substances Svo, *3 50 

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Wright, H. E. Handy Book for Brewers Svo, *5 00 

Wright, F. W. Design of a Condensing Plant i2mo, *i 50 

Wright, T. W. Elements of Mechanics Svo, *2 50 

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Zatiner, R. Transmission of Power. (Science Series No. 40.) .... i6mo, 

Zeidler, J., and Lustgarten, J. Electric Arc Lamps 8vo, *2 00 

Zeuner, A. Technical Thermodynamics. Trans, by J. F. Klein. Two 

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